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Internet Calendaring and Scheduling Core Object Specification (iCalendar)
draft-ietf-calsify-rfc2445bis-10

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 5545.
Author Bernard Desruisseaux
Last updated 2020-01-21 (Latest revision 2009-04-19)
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
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Responsible AD Lisa M. Dusseault
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draft-ietf-calsify-rfc2445bis-10
Network Working Group                               B. Desruisseaux, Ed.
Internet-Draft                                                    Oracle
Obsoletes: 2445 (if approved)                             April 20, 2009
Intended status: Standards Track
Expires: October 22, 2009

     Internet Calendaring and Scheduling Core Object Specification
                              (iCalendar)
                    draft-ietf-calsify-rfc2445bis-10

Status of This Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may contain material
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Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

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Abstract

   This document defines the iCalendar data format for representing and
   exchanging calendaring and scheduling information such as events, to-
   dos, journal entries and free/busy information, independent of any
   particular calendar service or protocol.

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Editorial Note (To be removed by RFC Editor prior to publication)

   This document is a product of the Calendaring and Scheduling
   Standards Simplification (Calsify) working group of the Internet
   Engineering Task Force.  Comments on this draft are welcomed, and
   should be addressed to the ietf-calsify@osafoundation.org [1] mailing
   list.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   8
   2.  Basic Grammar and Conventions . . . . . . . . . . . . . . . .   9
     2.1.  Formatting Conventions  . . . . . . . . . . . . . . . . .   9
     2.2.  Related Memos . . . . . . . . . . . . . . . . . . . . . .  10
   3.  iCalendar Object Specification  . . . . . . . . . . . . . . .  11
     3.1.  Content Lines . . . . . . . . . . . . . . . . . . . . . .  11
       3.1.1.  List and Field Separators . . . . . . . . . . . . . .  13
       3.1.2.  Multiple Values . . . . . . . . . . . . . . . . . . .  14
       3.1.3.  Binary Content  . . . . . . . . . . . . . . . . . . .  14
       3.1.4.  Character Set . . . . . . . . . . . . . . . . . . . .  15
     3.2.  Property Parameters . . . . . . . . . . . . . . . . . . .  15
       3.2.1.  Alternate Text Representation . . . . . . . . . . . .  16
       3.2.2.  Common Name . . . . . . . . . . . . . . . . . . . . .  17
       3.2.3.  Calendar User Type  . . . . . . . . . . . . . . . . .  18
       3.2.4.  Delegators  . . . . . . . . . . . . . . . . . . . . .  19
       3.2.5.  Delegatees  . . . . . . . . . . . . . . . . . . . . .  19
       3.2.6.  Directory Entry Reference . . . . . . . . . . . . . .  20
       3.2.7.  Inline Encoding . . . . . . . . . . . . . . . . . . .  20
       3.2.8.  Format Type . . . . . . . . . . . . . . . . . . . . .  21
       3.2.9.  Free/Busy Time Type . . . . . . . . . . . . . . . . .  22
       3.2.10. Language  . . . . . . . . . . . . . . . . . . . . . .  23
       3.2.11. Group or List Membership  . . . . . . . . . . . . . .  23
       3.2.12. Participation Status  . . . . . . . . . . . . . . . .  24
       3.2.13. Recurrence Identifier Range . . . . . . . . . . . . .  25
       3.2.14. Alarm Trigger Relationship  . . . . . . . . . . . . .  26
       3.2.15. Relationship Type . . . . . . . . . . . . . . . . . .  27
       3.2.16. Participation Role  . . . . . . . . . . . . . . . . .  28
       3.2.17. RSVP Expectation  . . . . . . . . . . . . . . . . . .  28
       3.2.18. Sent By . . . . . . . . . . . . . . . . . . . . . . .  29
       3.2.19. Time Zone Identifier  . . . . . . . . . . . . . . . .  29
       3.2.20. Value Data Types  . . . . . . . . . . . . . . . . . .  31
     3.3.  Property Value Data Types . . . . . . . . . . . . . . . .  32
       3.3.1.  Binary  . . . . . . . . . . . . . . . . . . . . . . .  32
       3.3.2.  Boolean . . . . . . . . . . . . . . . . . . . . . . .  33
       3.3.3.  Calendar User Address . . . . . . . . . . . . . . . .  33
       3.3.4.  Date  . . . . . . . . . . . . . . . . . . . . . . . .  34
       3.3.5.  Date-Time . . . . . . . . . . . . . . . . . . . . . .  34
       3.3.6.  Duration  . . . . . . . . . . . . . . . . . . . . . .  37

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       3.3.7.  Float . . . . . . . . . . . . . . . . . . . . . . . .  38
       3.3.8.  Integer . . . . . . . . . . . . . . . . . . . . . . .  39
       3.3.9.  Period of Time  . . . . . . . . . . . . . . . . . . .  39
       3.3.10. Recurrence Rule . . . . . . . . . . . . . . . . . . .  40
       3.3.11. Text  . . . . . . . . . . . . . . . . . . . . . . . .  48
       3.3.12. Time  . . . . . . . . . . . . . . . . . . . . . . . .  49
       3.3.13. URI . . . . . . . . . . . . . . . . . . . . . . . . .  51
       3.3.14. UTC Offset  . . . . . . . . . . . . . . . . . . . . .  52
     3.4.  iCalendar Object  . . . . . . . . . . . . . . . . . . . .  53
     3.5.  Property  . . . . . . . . . . . . . . . . . . . . . . . .  54
     3.6.  Calendar Components . . . . . . . . . . . . . . . . . . .  54
       3.6.1.  Event Component . . . . . . . . . . . . . . . . . . .  56
       3.6.2.  To-do Component . . . . . . . . . . . . . . . . . . .  60
       3.6.3.  Journal Component . . . . . . . . . . . . . . . . . .  62
       3.6.4.  Free/Busy Component . . . . . . . . . . . . . . . . .  64
       3.6.5.  Time Zone Component . . . . . . . . . . . . . . . . .  67
       3.6.6.  Alarm Component . . . . . . . . . . . . . . . . . . .  76
     3.7.  Calendar Properties . . . . . . . . . . . . . . . . . . .  81
       3.7.1.  Calendar Scale  . . . . . . . . . . . . . . . . . . .  81
       3.7.2.  Method  . . . . . . . . . . . . . . . . . . . . . . .  82
       3.7.3.  Product Identifier  . . . . . . . . . . . . . . . . .  83
       3.7.4.  Version . . . . . . . . . . . . . . . . . . . . . . .  84
     3.8.  Component Properties  . . . . . . . . . . . . . . . . . .  85
       3.8.1.  Descriptive Component Properties  . . . . . . . . . .  85
         3.8.1.1.  Attachment  . . . . . . . . . . . . . . . . . . .  85
         3.8.1.2.  Categories  . . . . . . . . . . . . . . . . . . .  86
         3.8.1.3.  Classification  . . . . . . . . . . . . . . . . .  87
         3.8.1.4.  Comment . . . . . . . . . . . . . . . . . . . . .  88
         3.8.1.5.  Description . . . . . . . . . . . . . . . . . . .  89
         3.8.1.6.  Geographic Position . . . . . . . . . . . . . . .  91
         3.8.1.7.  Location  . . . . . . . . . . . . . . . . . . . .  92
         3.8.1.8.  Percent Complete  . . . . . . . . . . . . . . . .  93
         3.8.1.9.  Priority  . . . . . . . . . . . . . . . . . . . .  94
         3.8.1.10. Resources . . . . . . . . . . . . . . . . . . . .  96
         3.8.1.11. Status  . . . . . . . . . . . . . . . . . . . . .  97
         3.8.1.12. Summary . . . . . . . . . . . . . . . . . . . . .  98
       3.8.2.  Date and Time Component Properties  . . . . . . . . . 100
         3.8.2.1.  Date/Time Completed . . . . . . . . . . . . . . . 100
         3.8.2.2.  Date/Time End . . . . . . . . . . . . . . . . . . 100
         3.8.2.3.  Date/Time Due . . . . . . . . . . . . . . . . . . 102
         3.8.2.4.  Date/Time Start . . . . . . . . . . . . . . . . . 103
         3.8.2.5.  Duration  . . . . . . . . . . . . . . . . . . . . 104
         3.8.2.6.  Free/Busy Time  . . . . . . . . . . . . . . . . . 105
         3.8.2.7.  Time Transparency . . . . . . . . . . . . . . . . 106
       3.8.3.  Time Zone Component Properties  . . . . . . . . . . . 107
         3.8.3.1.  Time Zone Identifier  . . . . . . . . . . . . . . 107
         3.8.3.2.  Time Zone Name  . . . . . . . . . . . . . . . . . 109
         3.8.3.3.  Time Zone Offset From . . . . . . . . . . . . . . 110

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         3.8.3.4.  Time Zone Offset To . . . . . . . . . . . . . . . 110
         3.8.3.5.  Time Zone URL . . . . . . . . . . . . . . . . . . 111
       3.8.4.  Relationship Component Properties . . . . . . . . . . 112
         3.8.4.1.  Attendee  . . . . . . . . . . . . . . . . . . . . 112
         3.8.4.2.  Contact . . . . . . . . . . . . . . . . . . . . . 115
         3.8.4.3.  Organizer . . . . . . . . . . . . . . . . . . . . 117
         3.8.4.4.  Recurrence ID . . . . . . . . . . . . . . . . . . 118
         3.8.4.5.  Related To  . . . . . . . . . . . . . . . . . . . 121
         3.8.4.6.  Uniform Resource Locator  . . . . . . . . . . . . 122
         3.8.4.7.  Unique Identifier . . . . . . . . . . . . . . . . 123
       3.8.5.  Recurrence Component Properties . . . . . . . . . . . 124
         3.8.5.1.  Exception Date/Times  . . . . . . . . . . . . . . 124
         3.8.5.2.  Recurrence Date/Times . . . . . . . . . . . . . . 126
         3.8.5.3.  Recurrence Rule . . . . . . . . . . . . . . . . . 128
       3.8.6.  Alarm Component Properties  . . . . . . . . . . . . . 138
         3.8.6.1.  Action  . . . . . . . . . . . . . . . . . . . . . 138
         3.8.6.2.  Repeat Count  . . . . . . . . . . . . . . . . . . 139
         3.8.6.3.  Trigger . . . . . . . . . . . . . . . . . . . . . 139
       3.8.7.  Change Management Component Properties  . . . . . . . 142
         3.8.7.1.  Date/Time Created . . . . . . . . . . . . . . . . 142
         3.8.7.2.  Date/Time Stamp . . . . . . . . . . . . . . . . . 143
         3.8.7.3.  Last Modified . . . . . . . . . . . . . . . . . . 144
         3.8.7.4.  Sequence Number . . . . . . . . . . . . . . . . . 145
       3.8.8.  Miscellaneous Component Properties  . . . . . . . . . 146
         3.8.8.1.  IANA Properties . . . . . . . . . . . . . . . . . 146
         3.8.8.2.  Non-standard Properties . . . . . . . . . . . . . 146
         3.8.8.3.  Request Status  . . . . . . . . . . . . . . . . . 148
   4.  iCalendar Object Examples . . . . . . . . . . . . . . . . . . 151
   5.  Recommended Practices . . . . . . . . . . . . . . . . . . . . 156
   6.  Internationalization Considerations . . . . . . . . . . . . . 157
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . 158
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 159
     8.1.  iCalendar Media Type Registration . . . . . . . . . . . . 159
     8.2.  New iCalendar Elements Registration . . . . . . . . . . . 162
       8.2.1.  iCalendar Elements Registration Procedure . . . . . . 162
       8.2.2.  Registration Template for Components  . . . . . . . . 162
       8.2.3.  Registration Template for Properties  . . . . . . . . 163
       8.2.4.  Registration Template for Parameters  . . . . . . . . 164
       8.2.5.  Registration Template for Value Data Types  . . . . . 164
       8.2.6.  Registration Template for Values  . . . . . . . . . . 164
     8.3.  Initial iCalendar Elements Registries . . . . . . . . . . 165
       8.3.1.  Components Registry . . . . . . . . . . . . . . . . . 165
       8.3.2.  Properties Registry . . . . . . . . . . . . . . . . . 166
       8.3.3.  Parameters Registry . . . . . . . . . . . . . . . . . 168
       8.3.4.  Value Data Types Registry . . . . . . . . . . . . . . 170
       8.3.5.  Calendar User Types Registry  . . . . . . . . . . . . 170
       8.3.6.  Free/Busy Time Types Registry . . . . . . . . . . . . 171
       8.3.7.  Participation Statuses Registry . . . . . . . . . . . 171

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       8.3.8.  Relationship Types Registry . . . . . . . . . . . . . 172
       8.3.9.  Participation Roles Registry  . . . . . . . . . . . . 172
       8.3.10. Actions Registry  . . . . . . . . . . . . . . . . . . 173
       8.3.11. Classifications Registry  . . . . . . . . . . . . . . 173
       8.3.12. Methods Registry  . . . . . . . . . . . . . . . . . . 173
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 174
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . 175
     10.1. Normative References  . . . . . . . . . . . . . . . . . . 175
     10.2. Informative References  . . . . . . . . . . . . . . . . . 176
   Appendix A.  Differences from RFC 2445  . . . . . . . . . . . . . 179
     A.1.  New restrictions  . . . . . . . . . . . . . . . . . . . . 179
     A.2.  Restrictions removed  . . . . . . . . . . . . . . . . . . 179
     A.3.  Deprecated features . . . . . . . . . . . . . . . . . . . 179
   Appendix B.  Change Log (to be removed by RFC Editor prior to
                publication) . . . . . . . . . . . . . . . . . . . . 180
     B.1.  Changes in -10  . . . . . . . . . . . . . . . . . . . . . 180
     B.2.  Changes in -09  . . . . . . . . . . . . . . . . . . . . . 180
     B.3.  Changes in -08  . . . . . . . . . . . . . . . . . . . . . 181
     B.4.  Changes in -07  . . . . . . . . . . . . . . . . . . . . . 182
     B.5.  Changes in -06  . . . . . . . . . . . . . . . . . . . . . 183
     B.6.  Changes in -05  . . . . . . . . . . . . . . . . . . . . . 185
     B.7.  Changes in -04  . . . . . . . . . . . . . . . . . . . . . 185
     B.8.  Changes in -03  . . . . . . . . . . . . . . . . . . . . . 187
     B.9.  Changes in -02  . . . . . . . . . . . . . . . . . . . . . 187
     B.10. Changes in -01  . . . . . . . . . . . . . . . . . . . . . 188

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1.  Introduction

   The use of calendaring and scheduling has grown considerably in the
   last decade.  Enterprise and inter-enterprise business has become
   dependent on rapid scheduling of events and actions using this
   information technology.  This memo is intended to progress the level
   of interoperability possible between dissimilar calendaring and
   scheduling applications.  This memo defines a MIME content type for
   exchanging electronic calendaring and scheduling information.  The
   Internet Calendaring and Scheduling Core Object Specification, or
   iCalendar, allows for the capture and exchange of information
   normally stored within a calendaring and scheduling application; such
   as a Personal Information Manager (PIM) or a Group Scheduling
   product.

   The iCalendar format is suitable as an exchange format between
   applications or systems.  The format is defined in terms of a MIME
   content type.  This will enable the object to be exchanged using
   several transports, including but not limited to SMTP, HTTP, a file
   system, desktop interactive protocols such as the use of a memory-
   based clipboard or drag/drop interactions, point-to-point
   asynchronous communication, wired-network transport, or some form of
   unwired transport such as infrared might also be used.

   The memo also provides for the definition of iCalendar object methods
   that will map this content type to a set of messages for supporting
   calendaring and scheduling operations such as requesting, replying
   to, modifying, and canceling meetings or appointments, to-dos and
   journal entries.  The iCalendar object methods can be used to define
   other calendaring and scheduling operations such a requesting for and
   replying with free/busy time data.  Such a scheduling protocol is
   defined in the iCalendar Transport-independent Interoperability
   Protocol (iTIP) defined in [I-D.ietf-calsify-2446bis].

   The memo also includes a formal grammar for the content type based on
   the Internet ABNF defined in [RFC5234].  This ABNF is required for
   the implementation of parsers and to serve as the definitive
   reference when ambiguities or questions arise in interpreting the
   descriptive prose definition of the memo.  Additional restrictions
   that could not easily be expressed with the ABNF syntax are specified
   as comments in the ABNF.  Comments with normative statements should
   be treated as such.

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2.  Basic Grammar and Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This memo makes use of both a descriptive prose and a more formal
   notation for defining the calendaring and scheduling format.

   The notation used in this memo is the ABNF notation of [RFC5234].
   Readers intending on implementing the format defined in this memo
   should be familiar with this notation in order to properly interpret
   the specifications of this memo.

   All numeric values used in this memo are given in decimal notation.

   All names of properties, property parameters, enumerated property
   values and property parameter values are case-insensitive.  However,
   all other property values are case-sensitive, unless otherwise
   stated.

      Note: All indented editorial notes, such as this one, are intended
      to provide the reader with additional information.  The
      information is not essential to the building of an implementation
      conformant with this memo.  The information is provided to
      highlight a particular feature or characteristic of the memo.

   The format for the iCalendar object is based on the syntax of the
   text/directory media type [RFC2425].  While the iCalendar object is
   not a profile of the text/directory media type [RFC2425], it does
   reuse a number of the elements from the [RFC2425] specification.

2.1.  Formatting Conventions

   The elements defined in this memo are defined in prose.  Many of the
   terms used to describe these have common usage that is different than
   the standards usage of this memo.  In order to reference within this
   memo elements of the calendaring and scheduling model, core object
   (this memo) or interoperability protocol [I-D.ietf-calsify-2446bis]
   some formatting conventions have been used.  Calendaring and
   scheduling roles are referred to in quoted-strings of text with the
   first character of each word in upper case.  For example, "Organizer"
   refers to a role of a "Calendar User" within the scheduling protocol
   defined by [I-D.ietf-calsify-2446bis].  Calendar components defined
   by this memo are referred to with capitalized, quoted-strings of
   text.  All calendar components start with the letter "V".  For
   example, "VEVENT" refers to the event calendar component, "VTODO"
   refers to the to-do calendar component and "VJOURNAL" refers to the

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   daily journal calendar component.  Scheduling methods defined by iTIP
   [I-D.ietf-calsify-2446bis] are referred to with capitalized, quoted-
   strings of text.  For example, "REQUEST" refers to the method for
   requesting a scheduling calendar component be created or modified,
   "REPLY" refers to the method a recipient of a request uses to update
   their status with the "Organizer" of the calendar component.

   The properties defined by this memo are referred to with capitalized,
   quoted-strings of text, followed by the word "property".  For
   example, "ATTENDEE" property refers to the iCalendar property used to
   convey the calendar address of a calendar user.  Property parameters
   defined by this memo are referred to with lowercase, quoted-strings
   of text, followed by the word "parameter".  For example, "value"
   parameter refers to the iCalendar property parameter used to override
   the default value type for a property value.  Enumerated values
   defined by this memo are referred to with capitalized text, either
   alone or followed by the word "value".  For example, the "MINUTELY"
   value can be used with the "FREQ" component of the "RECUR" value type
   to specify repeating components based on an interval of one minute or
   more.

   In this document, descriptions of characters are of the form
   "character name (codepoint)", where "codepoint" is from the US-ASCII
   character set.  The "character name" is the authoritative
   description; (codepoint) is a reference to that character in US-
   ASCII.

2.2.  Related Memos

   Implementers will need to be familiar with several other memos that,
   along with this memo, form a framework for Internet calendaring and
   scheduling standards.  This memo specifies a core specification of
   objects, value types, properties and property parameters.

   o  iTIP [I-D.ietf-calsify-2446bis] specifies an interoperability
      protocol for scheduling between different implementations;

   o  iMIP [I-D.ietf-calsify-rfc2447bis] specifies an Internet email
      binding for [I-D.ietf-calsify-2446bis].

   This memo does not attempt to repeat the specification of concepts or
   definitions from these other memos.  Where possible, references are
   made to the memo that provides for the specification of these
   concepts or definitions.

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3.  iCalendar Object Specification

   The following sections define the details of a Calendaring and
   Scheduling Core Object Specification.  The Calendaring and Scheduling
   Core Object is a collection of calendaring and scheduling
   information.  Typically, this information will consist of an
   iCalendar stream with one or more iCalendar objects.  The body of the
   iCalendar object consists of a sequence of calendar properties and
   one or more calendar components.

   Section 3.1 defines the content line format; Section 3.2 defines the
   property parameter format; Section 3.3 defines the data types for
   property values; Section 3.4 defines the iCalendar object format;
   Section 3.5 defines the iCalendar property format; Section 3.6
   defines the calendar component format; Section 3.7 defines calendar
   properties; and Section 3.8 defines calendar component properties.

   This information is intended to be an integral part of the MIME
   content type registration.  In addition, this information can be used
   independent of such content registration.  In particular, this memo
   has direct applicability for use as a calendaring and scheduling
   exchange format in file-, memory- or network-based transport
   mechanisms.

3.1.  Content Lines

   The iCalendar object is organized into individual lines of text,
   called content lines.  Content lines are delimited by a line break,
   which is a CRLF sequence (US-ASCII decimal 13, followed by US-ASCII
   decimal 10).

   Lines of text SHOULD NOT be longer than 75 octets, excluding the line
   break.  Long content lines SHOULD be split into a multiple line
   representations using a line "folding" technique.  That is, a long
   line can be split between any two characters by inserting a CRLF
   immediately followed by a single linear white space character (i.e.,
   SPACE, US-ASCII decimal 32 or HTAB, US-ASCII decimal 9).  Any
   sequence of CRLF followed immediately by a single linear white space
   character is ignored (i.e., removed) when processing the content
   type.

   For example the line:

      DESCRIPTION:This is a long description that exists on a long line.

   Can be represented as:

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      DESCRIPTION:This is a lo
       ng description
        that exists on a long line.

   The process of moving from this folded multiple line representation
   to its single line representation is called "unfolding".  Unfolding
   is accomplished by removing the CRLF character and the linear white
   space character that immediately follows.

   When parsing a content line, folded lines MUST first be unfolded
   according to the unfolding procedure described above.

      Note: It is possible for very simple implementations to generate
      improperly folded lines in the middle of a UTF-8 multi-octet
      sequence.  For this reason, implementations need to unfold lines
      in such a way to properly restore the original sequence.

   The content information associated with an iCalendar object is
   formatted using a syntax similar to that defined by [RFC2425].  That
   is, the content information consists of CRLF-separated content lines.

   The following notation defines the lines of content in an iCalendar
   object:

      contentline   = name *(";" param ) ":" value CRLF
      ; This ABNF is just a general definition for an initial parsing
      ; of the content line into its property name, parameter list,
      ; and value string

      ; When parsing a content line, folded lines MUST first
      ; be unfolded according to the unfolding procedure
      ; described above. When generating a content line, lines
      ; longer than 75 octets SHOULD be folded according to
      ; the folding procedure described above.

      name          = iana-token / x-name

      iana-token    = 1*(ALPHA / DIGIT / "-")
      ; iCalendar identifier registered with IANA

      x-name        = "X-" [vendorid "-"] 1*(ALPHA / DIGIT / "-")
      ; Reserved for experimental use.

      vendorid      = 3*(ALPHA / DIGIT)
      ; Vendor identification

      param         = param-name "=" param-value *("," param-value)
      ; Each property defines the specific ABNF for the parameters

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      ; allowed on the property. Refer to specific properties for
      ; precise parameter ABNF.

      param-name    = iana-token / x-name

      param-value   = paramtext / quoted-string

      paramtext     = *SAFE-CHAR

      value         = *VALUE-CHAR

      quoted-string = DQUOTE *QSAFE-CHAR DQUOTE

      QSAFE-CHAR    = WSP / %x21 / %x23-7E / NON-US-ASCII
      ; Any character except CONTROL and DQUOTE

      SAFE-CHAR     = WSP / %x21 / %x23-2B / %x2D-39 / %x3C-7E
                    / NON-US-ASCII
      ; Any character except CONTROL, DQUOTE, ";", ":", ","

      VALUE-CHAR    = WSP / %x21-7E / NON-US-ASCII
      ; Any textual character

      NON-US-ASCII  = UTF8-2 / UTF8-3 / UTF8-4
      ; UTF8-2, UTF8-3, and UTF8-4 are defined in [RFC3629]

      CONTROL       = %x00-08 / %x0A-1F / %x7F
      ; All the controls except HTAB

   The property value component of a content line has a format that is
   property specific.  Refer to the section describing each property for
   a definition of this format.

   All names of properties, property parameters, enumerated property
   values and property parameter values are case-insensitive.  However,
   all other property values are case-sensitive, unless otherwise
   stated.

3.1.1.  List and Field Separators

   Some properties and parameters allow a list of values.  Values in a
   list of values MUST be separated by a COMMA character (US-ASCII
   decimal 44).  There is no significance to the order of values in a
   list.  For those parameter values (such as those that specify URI
   values) that are specified in quoted-strings, the individual quoted-
   strings are separated by a COMMA character (US-ASCII decimal 44).

   Some property values are defined in terms of multiple parts.  These

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   structured property values MUST have their value parts separated by a
   SEMICOLON character (US-ASCII decimal 59).

   Some properties allow a list of parameters.  Each property parameter
   in a list of property parameters MUST be separated by a SEMICOLON
   character (US-ASCII decimal 59).

   Property parameters with values containing a COLON character (US-
   ASCII decimal 58), a SEMICOLON character (US-ASCII decimal 59) or a
   COMMA character (US-ASCII decimal 44) MUST be placed in quoted text.

   For example, in the following properties a SEMICOLON is used to
   separate property parameters from each other, and a COMMA is used to
   separate property values in a value list.

      ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT:mailto:
       jsmith@example.com

      RDATE;VALUE=DATE:19970304,19970504,19970704,19970904

3.1.2.  Multiple Values

   Some properties defined in the iCalendar object can have multiple
   values.  The general rule for encoding multi-valued items is to
   simply create a new content line for each value, including the
   property name.  However, it should be noted that some properties
   support encoding multiple values in a single property by separating
   the values with a COMMA character (US-ASCII decimal 44).  Individual
   property definitions should be consulted for determining whether a
   specific property allows multiple values and in which of these two
   forms.  Multi-valued properties MUST NOT be used to specify multiple
   language variants of the same value.  Calendar applications SHOULD
   display all values.

3.1.3.  Binary Content

   Binary content information in an iCalendar object SHOULD be
   referenced using a URI within a property value.  That is the binary
   content information SHOULD be placed in an external MIME entity that
   can be referenced by a URI from within the iCalendar object.  In
   applications where this is not feasible, binary content information
   can be included within an iCalendar object, but only after first
   encoding it into text using the "BASE64" encoding method defined in
   [RFC4648].  Inline binary content SHOULD only be used in applications
   whose special circumstances demand that an iCalendar object be
   expressed as a single entity.  A property containing inline binary
   content information MUST specify the "ENCODING" property parameter.
   Binary content information placed external to the iCalendar object

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   MUST be referenced by a uniform resource identifier (URI).

   The following example specifies an "ATTACH" property that references
   an attachment external to the iCalendar object with a URI reference:

      ATTACH:http://example.com/public/quarterly-report.doc

   The following example specifies an "ATTACH" property with inline
   binary encoded content information:

      ATTACH;FMTTYPE=text/plain;ENCODING=BASE64;VALUE=BINARY:VGhlIH
       F1aWNrIGJyb3duIGZveCBqdW1wcyBvdmVyIHRoZSBsYXp5IGRvZy4

3.1.4.  Character Set

   There is not a property parameter to declare the charset used in a
   property value.  The default charset for an iCalendar stream is UTF-8
   as defined in [RFC3629].

   The "charset" Content-Type parameter MUST be used in MIME transports
   to specify the charset being used.

3.2.  Property Parameters

   A property can have attributes associated with it.  These "property
   parameters" contain meta-information about the property or the
   property value.  Property parameters are provided to specify such
   information as the location of an alternate text representation for a
   property value, the language of a text property value, the value type
   of the property value and other attributes.

   Property parameter values that contain the COLON (US-ASCII decimal
   58), SEMICOLON (US-ASCII decimal 59) or COMMA (US-ASCII decimal 44)
   character separators MUST be specified as quoted-string text values.
   Property parameter values MUST NOT contain the DQUOTE (US-ASCII
   decimal 22) character.  The DQUOTE (US-ASCII decimal 22) character is
   used as a delimiter for parameter values that contain restricted
   characters or URI text.  For example:

      DESCRIPTION;ALTREP="cid:part1.0001@example.org":The Fall'98 Wild
        Wizards Conference - - Las Vegas\, NV\, USA

   Property parameter values that are not in quoted strings are case
   insensitive.

   The general property parameters defined by this memo are defined by
   the following notation:

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      icalparameter = altrepparam       ; Alternate text representation
                    / cnparam           ; Common name
                    / cutypeparam       ; Calendar user type
                    / delfromparam      ; Delegator
                    / deltoparam        ; Delegatee
                    / dirparam          ; Directory entry
                    / encodingparam     ; Inline encoding
                    / fmttypeparam      ; Format type
                    / fbtypeparam       ; Free/busy time type
                    / languageparam     ; Language for text
                    / memberparam       ; Group or list membership
                    / partstatparam     ; Participation status
                    / rangeparam        ; Recurrence identifier range
                    / trigrelparam      ; Alarm trigger relationship
                    / reltypeparam      ; Relationship type
                    / roleparam         ; Participation role
                    / rsvpparam         ; RSVP expectation
                    / sentbyparam       ; Sent by
                    / tzidparam         ; Reference to time zone object
                    / valuetypeparam    ; Property value data type
                    / other-param

      other-param   = (iana-param / x-param)

      iana-param  = iana-token "=" param-value *("," param-value)
      ; Some other IANA registered iCalendar parameter.

      x-param     = x-name "=" param-value *("," param-value)
      ; A non-standard, experimental parameter.

   Applications MUST ignore x-param and iana-param value they don't
   recognized.

3.2.1.  Alternate Text Representation

   Parameter Name:  ALTREP

   Purpose:  To specify an alternate text representation for the
      property value.

   Format Definition:  This property parameter is defined by the
      following notation:

      altrepparam = "ALTREP" "=" DQUOTE uri DQUOTE

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   Description:  This parameter specifies a URI that points to an
      alternate representation for a textual property value.  A property
      specifying this parameter MUST also include a value that reflects
      the default representation of the text value.  The URI parameter
      value MUST be specified in a quoted-string.

         Note: While there is no restriction imposed on the URI schemes
         allowed for this parameter, CID [RFC2392], HTTP [RFC2616], and
         HTTPS [RFC2818] are the URI schemes most commonly used by
         current implementations.

   Example:

        DESCRIPTION;ALTREP="CID:part3.msg.970415T083000@example.com":
         Project XYZ Review Meeting will include the following agenda
          items: (a) Market Overview\, (b) Finances\, (c) Project Man
         agement

      The "ALTREP" property parameter value might point to a "text/html"
      content portion.

        Content-Type:text/html
        Content-Id:<part3.msg.970415T083000@example.com>

        <html>
          <head>
           <title></title>
          </head>
          <body>
            <p>
              <b>Project XYZ Review Meeting</b> will include
              the following agenda items:
              <ol>
                <li>Market Overview</li>
                <li>Finances</li>
                <li>Project Management</li>
              </ol>
            </p>
          </body>
        </html>

3.2.2.  Common Name

   Parameter Name:  CN

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   Purpose:  To specify the common name to be associated with the
      calendar user specified by the property.

   Format Definition:  This property parameter is defined by the
      following notation:

      cnparam    = "CN" "=" param-value

   Description:  This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter specifies the common name
      to be associated with the calendar user specified by the property.
      The parameter value is text.  The parameter value can be used for
      display text to be associated with the calendar address specified
      by the property.

   Example:

        ORGANIZER;CN="John Smith":mailto:jsmith@example.com

3.2.3.  Calendar User Type

   Parameter Name:  CUTYPE

   Purpose:  To specify the type of calendar user specified by the
      property.

   Format Definition:  This property parameter is defined by the
      following notation:

        cutypeparam        = "CUTYPE" "="
                           ("INDIVIDUAL"   ; An individual
                          / "GROUP"        ; A group of individuals
                          / "RESOURCE"     ; A physical resource
                          / "ROOM"         ; A room resource
                          / "UNKNOWN"      ; Otherwise not known
                          / x-name         ; Experimental type
                          / iana-token)    ; Other IANA registered
                                           ; type
        ; Default is INDIVIDUAL

   Description:  This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter identifies the type of
      calendar user specified by the property.  If not specified on a
      property that allows this parameter, the default is INDIVIDUAL.
      Applications MUST treat x-name and iana-token value they don't
      recognized the same way as they would the UNKNOWN value.

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   Example:

        ATTENDEE;CUTYPE=GROUP:mailto:ietf-calsch@example.org

3.2.4.  Delegators

   Parameter Name:  DELEGATED-FROM

   Purpose:  To specify the calendar users that have delegated their
      participation to the calendar user specified by the property.

   Format Definition:  This property parameter is defined by the
      following notation:

        delfromparam       = "DELEGATED-FROM" "=" DQUOTE cal-address
                              DQUOTE *("," DQUOTE cal-address DQUOTE)

   Description:  This parameter can be specified on properties with a
      CAL-ADDRESS value type.  This parameter specifies those calendar
      users that have delegated their participation in a group scheduled
      event or to-do to the calendar user specified by the property.
      The individual calendar address parameter values MUST each be
      specified in a quoted-string.

   Example:

        ATTENDEE;DELEGATED-FROM="mailto:jsmith@example.com":mailto:
         jdoe@example.com

3.2.5.  Delegatees

   Parameter Name:  DELEGATED-TO

   Purpose:  To specify the calendar users to whom the calendar user
      specified by the property has delegated participation.

   Format Definition:  This property parameter is defined by the
      following notation:

        deltoparam = "DELEGATED-TO" "=" DQUOTE cal-address DQUOTE
                     *("," DQUOTE cal-address DQUOTE)

   Description:  This parameter can be specified on properties with a
      CAL-ADDRESS value type.  This parameter specifies those calendar
      users whom have been delegated participation in a group scheduled
      event or to-do by the calendar user specified by the property.
      The individual calendar address parameter values MUST each be
      specified in a quoted-string.

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   Example:

        ATTENDEE;DELEGATED-TO="mailto:jdoe@example.com","mailto:jqpublic
         @example.com":mailto:jsmith@example.com

3.2.6.  Directory Entry Reference

   Parameter Name:  DIR

   Purpose:  To specify reference to a directory entry associated with
      the calendar user specified by the property.

   Format Definition:  This property parameter is defined by the
      following notation:

        dirparam   = "DIR" "=" DQUOTE uri DQUOTE

   Description:  This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter specifies a reference to
      the directory entry associated with the calendar user specified by
      the property.  The parameter value is a URI.  The URI parameter
      value MUST be specified in a quoted-string.

         Note: While there is no restriction imposed on the URI schemes
         allowed for this parameter, CID [RFC2392], DATA [RFC2397], FILE
         [RFC1738], FTP [RFC1738], HTTP [RFC2616], HTTPS [RFC2818], LDAP
         [RFC4516], and MID [RFC2392] are the URI schemes most commonly
         used by current implementations.

   Example:

        ORGANIZER;DIR="ldap://example.com:6666/o=ABC%20Industries,
         c=US???(cn=Jim%20Dolittle)":mailto:jimdo@example.com

3.2.7.  Inline Encoding

   Parameter Name:  ENCODING

   Purpose:  To specify an alternate inline encoding for the property
      value.

   Format Definition:  This property parameter is defined by the
      following notation:

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        encodingparam      = "ENCODING" "="
                           ( "8BIT"
           ; "8bit" text encoding is defined in [RFC2045]
                           / "BASE64"
           ; "BASE64" binary encoding format is defined in [RFC4648]
                           )

   Description:  This property parameter identifies the inline encoding
      used in a property value.  The default encoding is "8BIT",
      corresponding to a property value consisting of text.  The
      "BASE64" encoding type corresponds to a property value encoded
      using the "BASE64" encoding defined in [RFC2045].

      If the value type parameter is ";VALUE=BINARY", then the inline
      encoding parameter MUST be specified with the value
      ";ENCODING=BASE64".

   Example:

      ATTACH;FMTTYPE=text/plain;ENCODING=BASE64;VALUE=BINARY:TG9yZW
       0gaXBzdW0gZG9sb3Igc2l0IGFtZXQsIGNvbnNlY3RldHVyIGFkaXBpc2ljaW
       5nIGVsaXQsIHNlZCBkbyBlaXVzbW9kIHRlbXBvciBpbmNpZGlkdW50IHV0IG
       xhYm9yZSBldCBkb2xvcmUgbWFnbmEgYWxpcXVhLiBVdCBlbmltIGFkIG1pbm
       ltIHZlbmlhbSwgcXVpcyBub3N0cnVkIGV4ZXJjaXRhdGlvbiB1bGxhbWNvIG
       xhYm9yaXMgbmlzaSB1dCBhbGlxdWlwIGV4IGVhIGNvbW1vZG8gY29uc2VxdW
       F0LiBEdWlzIGF1dGUgaXJ1cmUgZG9sb3IgaW4gcmVwcmVoZW5kZXJpdCBpbi
       B2b2x1cHRhdGUgdmVsaXQgZXNzZSBjaWxsdW0gZG9sb3JlIGV1IGZ1Z2lhdC
       BudWxsYSBwYXJpYXR1ci4gRXhjZXB0ZXVyIHNpbnQgb2NjYWVjYXQgY3VwaW
       RhdGF0IG5vbiBwcm9pZGVudCwgc3VudCBpbiBjdWxwYSBxdWkgb2ZmaWNpYS
       BkZXNlcnVudCBtb2xsaXQgYW5pbSBpZCBlc3QgbGFib3J1bS4=

3.2.8.  Format Type

   Parameter Name:  FMTTYPE

   Purpose:  To specify the content type of a referenced object.

   Format Definition:  This property parameter is defined by the
      following notation:

        fmttypeparam = "FMTTYPE" "=" type-name "/" subtype-name
                       ; Where "type-name" and "subtype-name" are
                       ; defined in section 4.2 of [RFC4288]

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   Description:  This parameter can be specified on properties that are
      used to reference an object.  The parameter specifies the media
      type [RFC4288] of the referenced object.  For example, on the
      "ATTACH" property, a FTP type URI value does not, by itself,
      necessarily convey the type of content associated with the
      resource.  The parameter value MUST be the text for either an IANA
      registered media type or a non-standard media type.

   Example:

        ATTACH;FMTTYPE=application/msword:ftp://example.com/pub/docs/
         agenda.doc

3.2.9.  Free/Busy Time Type

   Parameter Name:  FBTYPE

   Purpose:  To specify the free or busy time type.

   Format Definition:  This property parameter is defined by the
      following notation:

        fbtypeparam        = "FBTYPE" "=" ("FREE" / "BUSY"
                           / "BUSY-UNAVAILABLE" / "BUSY-TENTATIVE"
                           / x-name
                 ; Some experimental iCalendar free busy type.
                           / iana-token)
                 ; Some other IANA registered iCalendar free busy type.

   Description:  This parameter specifies the free or busy time type.
      The value FREE indicates that the time interval is free for
      scheduling.  The value BUSY indicates that the time interval is
      busy because one or more events have been scheduled for that
      interval.  The value BUSY-UNAVAILABLE indicates that the time
      interval is busy and that the interval can not be scheduled.  The
      value BUSY-TENTATIVE indicates that the time interval is busy
      because one or more events have been tentatively scheduled for
      that interval.  If not specified on a property that allows this
      parameter, the default is BUSY.  Applications MUST treat x-name
      and iana-token value they don't recognized the same way as they
      would the BUSY value.

   Example:  The following is an example of this parameter on a
      "FREEBUSY" property.

        FREEBUSY;FBTYPE=BUSY:19980415T133000Z/19980415T170000Z

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3.2.10.  Language

   Parameter Name:  LANGUAGE

   Purpose:  To specify the language for text values in a property or
      property parameter.

   Format Definition:  This property parameter is defined by the
      following notation:

        languageparam = "LANGUAGE" "=" language

        language = Language-Tag
                   ; As defined in [RFC4646]

   Description:  This parameter identifies the language of the text in
      the property value and of all property parameter values of the
      property.  The value of the "LANGUAGE" property parameter is that
      defined in [RFC4646].

      For transport in a MIME entity, the Content-Language header field
      can be used to set the default language for the entire body part.
      Otherwise, no default language is assumed.

   Example:  The following are examples of this parameter on the
      "SUMMARY" and "LOCATION" properties:

        SUMMARY;LANGUAGE=en-US:Company Holiday Party

        LOCATION;LANGUAGE=en:Germany

        LOCATION;LANGUAGE=no:Tyskland

3.2.11.  Group or List Membership

   Parameter Name:  MEMBER

   Purpose:  To specify the group or list membership of the calendar
      user specified by the property.

   Format Definition:  This property parameter is defined by the
      following notation:

        memberparam        = "MEMBER" "=" DQUOTE cal-address DQUOTE
                             *("," DQUOTE cal-address DQUOTE)

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   Description:  This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter identifies the groups or
      list membership for the calendar user specified by the property.
      The parameter value is either a single calendar address in a
      quoted-string or a COMMA character (US-ASCII decimal 44) separated
      list of calendar addresses, each in a quoted-string.  The
      individual calendar address parameter values MUST each be
      specified in a quoted-string.

   Example:

        ATTENDEE;MEMBER="mailto:ietf-calsch@example.org":mailto:
         jsmith@example.com

        ATTENDEE;MEMBER="mailto:projectA@example.com","mailto:pr
         ojectB@example.com":mailto:janedoe@example.com

3.2.12.  Participation Status

   Parameter Name:  PARTSTAT

   Purpose:  To specify the participation status for the calendar user
      specified by the property.

   Format Definition:  This property parameter is defined by the
      following notation:

        partstatparam    = "PARTSTAT" "="
                          (partstat-event
                         / partstat-todo
                         / partstat-jour)

        partstat-event   = ("NEEDS-ACTION"    ; Event needs action
                         / "ACCEPTED"         ; Event accepted
                         / "DECLINED"         ; Event declined
                         / "TENTATIVE"        ; Event tentatively
                                              ; accepted
                         / "DELEGATED"        ; Event delegated
                         / x-name             ; Experimental status
                         / iana-token)        ; Other IANA registered
                                              ; status
        ; These are the participation statuses for a "VEVENT".
        ; Default is NEEDS-ACTION.

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        partstat-todo    = ("NEEDS-ACTION"    ; To-do needs action
                         / "ACCEPTED"         ; To-do accepted
                         / "DECLINED"         ; To-do declined
                         / "TENTATIVE"        ; To-do tentatively
                                              ; accepted
                         / "DELEGATED"        ; To-do delegated
                         / "COMPLETED"        ; To-do completed.
                                              ; COMPLETED property has
                                              ; date/time completed.
                         / "IN-PROCESS"       ; To-do in process of
                                              ; being completed
                         / x-name             ; Experimental status
                         / iana-token)        ; Other IANA registered
                                              ; status
        ; These are the participation statuses for a "VTODO".
        ; Default is NEEDS-ACTION.

        partstat-jour    = ("NEEDS-ACTION"    ; Journal needs action
                         / "ACCEPTED"         ; Journal accepted
                         / "DECLINED"         ; Journal declined
                         / x-name             ; Experimental status
                         / iana-token)        ; Other IANA registered
                                              ; status
        ; These are the participation statuses for a "VJOURNAL".
        ; Default is NEEDS-ACTION.

   Description:  This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter identifies the
      participation status for the calendar user specified by the
      property value.  The parameter values differ depending on whether
      they are associated with a group scheduled "VEVENT", "VTODO" or
      "VJOURNAL".  The values MUST match one of the values allowed for
      the given calendar component.  If not specified on a property that
      allows this parameter, the default value is NEEDS-ACTION.
      Applications MUST treat x-name and iana-token value they don't
      recognized the same way as they would the NEEDS-ACTION value.

   Example:

        ATTENDEE;PARTSTAT=DECLINED:mailto:jsmith@example.com

3.2.13.  Recurrence Identifier Range

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   Parameter Name:  RANGE

   Purpose:  To specify the effective range of recurrence instances from
      the instance specified by the recurrence identifier specified by
      the property.

   Format Definition:  This property parameter is defined by the
      following notation:

        rangeparam = "RANGE" "=" "THISANDFUTURE"
        ; To specify the instance specified by the recurrence identifier
        ; and all subsequent recurrence instances

   Description:  This parameter can be specified on a property that
      specifies a recurrence identifier.  The parameter specifies the
      effective range of recurrence instances that is specified by the
      property.  The effective range is from the recurrence identifier
      specified by the property.  If this parameter is not specified on
      an allowed property, then the default range is the single instance
      specified by the recurrence identifier value of the property.  The
      parameter value can only be "THISANDFUTURE" to indicate a range
      defined by the recurrence identifier and all subsequent instances.
      The value "THISANDPRIOR" is deprecated by this revision of
      iCalendar and MUST NOT be generated by applications.

   Example:

        RECURRENCE-ID;RANGE=THISANDFUTURE:19980401T133000Z

3.2.14.  Alarm Trigger Relationship

   Parameter Name:  RELATED

   Purpose:  To specify the relationship of the alarm trigger with
      respect to the start or end of the calendar component.

   Format Definition:  This property parameter is defined by the
      following notation:

        trigrelparam       = "RELATED" "="
                            ("START"       ; Trigger off of start
                           / "END")        ; Trigger off of end

   Description:  This parameter can be specified on properties that
      specify an alarm trigger with a "DURATION" value type.  The
      parameter specifies whether the alarm will trigger relative to the
      start or end of the calendar component.  The parameter value START
      will set the alarm to trigger off the start of the calendar

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      component; the parameter value END will set the alarm to trigger
      off the end of the calendar component.  If the parameter is not
      specified on an allowable property, then the default is START.

   Example:

        TRIGGER;RELATED=END:PT5M

3.2.15.  Relationship Type

   Parameter Name:  RELTYPE

   Purpose:  To specify the type of hierarchical relationship associated
      with the calendar component specified by the property.

   Format Definition:  This property parameter is defined by the
      following notation:

        reltypeparam       = "RELTYPE" "="
                            ("PARENT"    ; Parent relationship. Default.
                           / "CHILD"     ; Child relationship
                           / "SIBLING"   ; Sibling relationship
                           / iana-token  ; Some other IANA registered
                                         ; iCalendar relationship type
                           / x-name)     ; A non-standard, experimental
                                         ; relationship type

   Description:  This parameter can be specified on a property that
      references another related calendar.  The parameter specifies the
      hierarchical relationship type of the calendar component
      referenced by the property.  The parameter value can be PARENT, to
      indicate that the referenced calendar component is a superior of
      calendar component; CHILD to indicate that the referenced calendar
      component is a subordinate of the calendar component; SIBLING to
      indicate that the referenced calendar component is a peer of the
      calendar component.  If this parameter is not specified on an
      allowable property, the default relationship type is PARENT.
      Applications MUST treat x-name and iana-token value they don't
      recognized the same way as they would the PARENT value.

   Example:

        RELATED-TO;RELTYPE=SIBLING:19960401-080045-4000F192713@
         example.com

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3.2.16.  Participation Role

   Parameter Name:  ROLE

   Purpose:  To specify the participation role for the calendar user
      specified by the property.

   Format Definition:  This property parameter is defined by the
      following notation:

        roleparam  = "ROLE" "="
                    ("CHAIR"             ; Indicates chair of the
                                         ; calendar entity
                   / "REQ-PARTICIPANT"   ; Indicates a participant whose
                                         ; participation is required
                   / "OPT-PARTICIPANT"   ; Indicates a participant whose
                                         ; participation is optional
                   / "NON-PARTICIPANT"   ; Indicates a participant who
                                         ; is copied for information
                                         ; purposes only
                   / x-name              ; Experimental role
                   / iana-token)         ; Other IANA role
        ; Default is REQ-PARTICIPANT

   Description:  This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter specifies the participation
      role for the calendar user specified by the property in the group
      schedule calendar component.  If not specified on a property that
      allows this parameter, the default value is REQ-PARTICIPANT.
      Applications MUST treat x-name and iana-token value they don't
      recognized the same way as they would the REQ-PARTICIPANT value.

   Example:

        ATTENDEE;ROLE=CHAIR:mailto:mrbig@example.com

3.2.17.  RSVP Expectation

   Parameter Name:  RSVP

   Purpose:  To specify whether there is an expectation of a favor of a
      reply from the calendar user specified by the property value.

   Format Definition:  This property parameter is defined by the
      following notation:

        rsvpparam = "RSVP" "=" ("TRUE" / "FALSE")
        ; Default is FALSE

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   Description:  This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter identifies the expectation
      of a reply from the calendar user specified by the property value.
      This parameter is used by the "Organizer" to request a
      participation status reply from an "Attendee" of a group scheduled
      event or to-do.  If not specified on a property that allows this
      parameter, the default value is FALSE.

   Example:

        ATTENDEE;RSVP=TRUE:mailto:jsmith@example.com

3.2.18.  Sent By

   Parameter Name:  SENT-BY

   Purpose:  To specify the calendar user that is acting on behalf of
      the calendar user specified by the property.

   Format Definition:  This property parameter is defined by the
      following notation:

        sentbyparam        = "SENT-BY" "=" DQUOTE cal-address DQUOTE

   Description:  This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter specifies the calendar user
      that is acting on behalf of the calendar user specified by the
      property.  The parameter value MUST be a mailto URI as defined in
      [RFC2368].  The individual calendar address parameter values MUST
      each be specified in a quoted-string.

   Example:

        ORGANIZER;SENT-BY="mailto:sray@example.com":mailto:
         jsmith@example.com

3.2.19.  Time Zone Identifier

   Parameter Name:  TZID

   Purpose:  To specify the identifier for the time zone definition for
      a time component in the property value.

   Format Definition:  This property parameter is defined by the
      following notation:

        tzidparam  = "TZID" "=" [tzidprefix] paramtext

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        tzidprefix = "/"

   Description:  This parameter MUST be specified on the "DTSTART",
      "DTEND", "DUE", "EXDATE" and "RDATE" properties when either a
      DATE-TIME or TIME value type is specified and when the value is
      not either a UTC or a "floating" time.  Refer to the DATE-TIME or
      TIME value type definition for a description of UTC and "floating
      time" formats.  This property parameter specifies a text value
      which uniquely identifies the "VTIMEZONE" calendar component to be
      used when evaluating the time portion of the property.  The value
      of the "TZID" property parameter will be equal to the value of the
      "TZID" property for the matching time zone definition.  An
      individual "VTIMEZONE" calendar component MUST be specified for
      each unique "TZID" parameter value specified in the iCalendar
      object.

      The parameter MUST be specified on properties with a DATE-TIME
      value if the DATE-TIME is not either a UTC or a "floating" time.

      The presence of the SOLIDUS character (US-ASCII decimal 47) as a
      prefix, indicates that this "TZID" represents a unique ID in a
      globally defined time zone registry (when such registry is
      defined).

         Note: This document does not define a naming convention for
         time zone identifiers.  Implementers may want to use the naming
         conventions defined in existing time zone specifications such
         as the public-domain TZ database [TZDB].  The specification of
         globally unique time zone identifiers is not addressed by this
         document and is left for future study.

      The following are examples of this property parameter:

        DTSTART;TZID=America/New_York:19980119T020000

        DTEND;TZID=America/New_York:19980119T030000

      The "TZID" property parameter MUST NOT be applied to DATE
      properties, and DATE-TIME or TIME properties whose time values are
      specified in UTC.

      The use of local time in a DATE-TIME or TIME value without the
      "TZID" property parameter is to be interpreted as floating time,
      regardless of the existence of "VTIMEZONE" calendar components in
      the iCalendar object.

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      For more information see the sections on the value types DATE-TIME
      and TIME.

3.2.20.  Value Data Types

   Parameter Name:  VALUE

   Purpose:  To explicitly specify the value type format for a property
      value.

   Format Definition:  This property parameter is defined by the
      following notation:

        valuetypeparam = "VALUE" "=" valuetype

        valuetype  = ("BINARY"
                   / "BOOLEAN"
                   / "CAL-ADDRESS"
                   / "DATE"
                   / "DATE-TIME"
                   / "DURATION"
                   / "FLOAT"
                   / "INTEGER"
                   / "PERIOD"
                   / "RECUR"
                   / "TEXT"
                   / "TIME"
                   / "URI"
                   / "UTC-OFFSET"
                   / x-name
                   ; Some experimental iCalendar value type.
                   / iana-token)
                   ; Some other IANA registered iCalendar value type.

   Description:  This parameter specifies the value type and format of
      the property value.  The property values MUST be of a single value
      type.  For example, a "RDATE" property cannot have a combination
      of DATE-TIME and TIME value types.

      If the property's value is the default value type, then this
      parameter need not be specified.  However, if the property's
      default value type is overridden by some other allowable value
      type, then this parameter MUST be specified.

      Applications MUST preserve the value data for x-name and iana-
      token values that they don't recognize without attempting to
      interpret or parse the value data.

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3.3.  Property Value Data Types

   The properties in an iCalendar object are strongly typed.  The
   definition of each property restricts the value to be one of the
   value data types, or simply value types, defined in this section.
   The value type for a property will either be specified implicitly as
   the default value type or will be explicitly specified with the
   "VALUE" parameter.  If the value type of a property is one of the
   alternate valid types, then it MUST be explicitly specified with the
   "VALUE" parameter.

3.3.1.  Binary

   Value Name:  BINARY

   Purpose:  This value type is used to identify properties that contain
      a character encoding of inline binary data.  For example, an
      inline attachment of a document might be included in an iCalendar
      object.

   Format Definition:  This value type is defined by the following
      notation:

        binary     = *(4b-char) [b-end]
        ; A "BASE64" encoded character string, as defined by [RFC4648].

        b-end      = (2b-char "==") / (3b-char "=")

        b-char = ALPHA / DIGIT / "+" / "/"

   Description:  Property values with this value type MUST also include
      the inline encoding parameter sequence of ";ENCODING=BASE64".
      That is, all inline binary data MUST first be character encoded
      using the "BASE64" encoding method defined in [RFC2045].  No
      additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) is defined for this value type.

   Example:  The following is an example of a "BASE64" encoded binary
      value data.

      ATTACH;FMTTYPE=image/vnd.microsoft.icon;ENCODING=BASE64;VALUE
       =BINARY:AAABAAEAEBAQAAEABAAoAQAAFgAAACgAAAAQAAAAIAAAAAEABAAA
       AAAAAAAAAAAAAAAAAAAAAAAAAAAAAACAAAAAgIAAAICAgADAwMAA////AAAA
       AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
       AAAAAAAAAAAAAAAAAAAAAAMwAAAAAAABNEMQAAAAAAAkQgAAAAAAJEREQgAA
       ACECQ0QgEgAAQxQzM0E0AABERCRCREQAADRDJEJEQwAAAhA0QwEQAAAAAERE
       AAAAAAAAREQAAAAAAAAkQgAAAAAAAAMgAAAAAAAAAAAAAAAAAAAAAAAAAAAA
       AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

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       AAAAAAAAAAAA

3.3.2.  Boolean

   Value Name:  BOOLEAN

   Purpose:  This value type is used to identify properties that contain
      either a "TRUE" or "FALSE" Boolean value.

   Format Definition:  This value type is defined by the following
      notation:

        boolean    = "TRUE" / "FALSE"

   Description:  These values are case insensitive text.  No additional
      content value encoding (i.e., BACKSLASH character encoding, see
      Section 3.3.11) is defined for this value type.

   Example:  The following is an example of a hypothetical property that
      has a BOOLEAN value type:

        TRUE

3.3.3.  Calendar User Address

   Value Name:  CAL-ADDRESS

   Purpose:  This value type is used to identify properties that contain
      a calendar user address.

   Format Definition:  This value type is defined by the following
      notation:

        cal-address        = uri

   Description:  The value is a URI as defined by [RFC3986] or any other
      IANA registered form for a URI.  When used to address an Internet
      email transport address for a calendar user, the value MUST be a
      mailto URI, as defined by [RFC2368].  No additional content value
      encoding (i.e., BACKSLASH character encoding, see Section 3.3.11)
      is defined for this value type.

   Example:

     mailto:jane_doe@example.com

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3.3.4.  Date

   Value Name:  DATE

   Purpose:  This value type is used to identify values that contain a
      calendar date.

   Format Definition:  This value type is defined by the following
      notation:

        date               = date-value

        date-value         = date-fullyear date-month date-mday
        date-fullyear      = 4DIGIT
        date-month         = 2DIGIT        ;01-12
        date-mday          = 2DIGIT        ;01-28, 01-29, 01-30, 01-31
                                           ;based on month/year

   Description:  If the property permits, multiple "date" values are
      specified as a COMMA character (US-ASCII decimal 44) separated
      list of values.  The format for the value type is based on the
      [ISO.8601.2004] complete representation, basic format for a
      calendar date.  The textual format specifies a four-digit year,
      two-digit month, and two-digit day of the month.  There are no
      separator characters between the year, month and day component
      text.

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) is defined for this value type.

   Example:  The following represents July 14, 1997:

        19970714

3.3.5.  Date-Time

   Value Name:  DATE-TIME

   Purpose:  This value type is used to identify values that specify a
      precise calendar date and time of day.

   Format Definition:  This value type is defined by the following
      notation:

        date-time  = date "T" time ;As specified in the date and time
                                   ;value definitions

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   Description:  If the property permits, multiple "date-time" values
      are specified as a COMMA character (US-ASCII decimal 44) separated
      list of values.  No additional content value encoding (i.e.,
      BACKSLASH character encoding, see Section 3.3.11) is defined for
      this value type.

      The "DATE-TIME" value type is used to identify values that contain
      a precise calendar date and time of day.  The format is based on
      the [ISO.8601.2004] complete representation, basic format for a
      calendar date and time of day.  The text format is a concatenation
      of the "date", followed by the LATIN CAPITAL LETTER T character
      (US-ASCII decimal 84) time designator, followed by the "time"
      format.

      The "DATE-TIME" value type expresses time values in three forms:

      The form of date and time with UTC offset MUST NOT be used.  For
      example, the following is not valid for a date-time value:

        19980119T230000-0800       ;Invalid time format

      FORM #1: DATE WITH LOCAL TIME

      The date with local time form is simply a DATE-TIME value that
      does not contain the UTC designator nor does it reference a time
      zone.  For example, the following represents January 18, 1998, at
      11 PM:

        19980118T230000

      DATE-TIME values of this type are said to be "floating" and are
      not bound to any time zone in particular.  They are used to
      represent the same hour, minute, and second value regardless of
      which time zone is currently being observed.  For example, an
      event can be defined that indicates that an individual will be
      busy from 11:00 AM to 1:00 PM every day, no matter which time zone
      the person is in.  In these cases, a local time can be specified.
      The recipient of an iCalendar object with a property value
      consisting of a local time, without any relative time zone
      information, SHOULD interpret the value as being fixed to whatever
      time zone the "ATTENDEE" is in at any given moment.  This means
      that two "Attendees", in different time zones, receiving the same
      event definition as a floating time, may be participating in the
      event at different actual times.  Floating time SHOULD only be
      used where that is the reasonable behavior.

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      In most cases, a fixed time is desired.  To properly communicate a
      fixed time in a property value, either UTC time or local time with
      time zone reference MUST be specified.

      The use of local time in a DATE-TIME value without the "TZID"
      property parameter is to be interpreted as floating time,
      regardless of the existence of "VTIMEZONE" calendar components in
      the iCalendar object.

      FORM #2: DATE WITH UTC TIME

      The date with UTC time, or absolute time, is identified by a LATIN
      CAPITAL LETTER Z suffix character (US-ASCII decimal 90), the UTC
      designator, appended to the time value.  For example, the
      following represents January 19, 1998, at 0700 UTC:

        19980119T070000Z

      The "TZID" property parameter MUST NOT be applied to DATE-TIME
      properties whose time values are specified in UTC.

      FORM #3: DATE WITH LOCAL TIME AND TIME ZONE REFERENCE

      The date and local time with reference to time zone information is
      identified by the use the "TZID" property parameter to reference
      the appropriate time zone definition.  "TZID" is discussed in
      detail in Section 3.2.19.  For example, the following represents
      2:00 A.M. in New York on Janurary 19, 1998:

        TZID=America/New_York:19980119T020000

      If, based on the definition of the referenced time zone, the local
      time described occurs more than once (when changing from daylight
      to standard time), the DATE-TIME value refers to the first
      occurence of the referenced time.  Thus, TZID=America/
      New_York:20071104T013000 indicates November 4, 2007 at 1:30 A.M.
      EDT (UTC-04:00).  If the local time described does not occur (when
      changing from standard to daylight time), the DATE-TIME value is
      interpreted using the UTC offset before the gap in local times.
      Thus, TZID=America/New_York:20070311T023000 indicates March 11,
      2007 at 3:30 A.M. EDT (UTC-04:00), one hour after 1:30 A.M. EST
      (UTC-05:00).

      A time value MUST only specify the second 60 when specifying a
      positive leap second.  For example:

        19970630T235960Z

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      Implementations which do not support leap seconds SHOULD interpret
      the second 60 as equivalent to the second 59.

   Example:  The following represents July 14, 1997, at 1:30 PM in New
      York City in each of the three time formats, using the "DTSTART"
      property.

        DTSTART:19970714T133000                   ; Local time
        DTSTART:19970714T173000Z                  ; UTC time
        DTSTART;TZID=America/New_York:19970714T133000
                                                  ; Local time and time
                                                  ; zone reference

3.3.6.  Duration

   Value Name:  DURATION

   Purpose:  This value type is used to identify properties that contain
      a duration of time.

   Format Definition:  This value type is defined by the following
      notation:

        dur-value  = (["+"] / "-") "P" (dur-date / dur-time / dur-week)

        dur-date   = dur-day [dur-time]
        dur-time   = "T" (dur-hour / dur-minute / dur-second)
        dur-week   = 1*DIGIT "W"
        dur-hour   = 1*DIGIT "H" [dur-minute]
        dur-minute = 1*DIGIT "M" [dur-second]
        dur-second = 1*DIGIT "S"
        dur-day    = 1*DIGIT "D"

   Description:  If the property permits, multiple "duration" values are
      specified by a COMMA character (US-ASCII decimal 44) separated
      list of values.  The format is based on the [ISO.8601.2004]
      complete representation basic format with designators for the
      duration of time.  The format can represent nominal durations
      (weeks and days) and accurate durations (hours, minutes, and
      seconds).  Note that unlike [ISO.8601.2004] this value type
      doesn't support the "Y" and "M" designators to specify durations
      in terms of years and months.

      The duration of a week or a day depends on its position in the
      calendar.  In the case of discontinuities in the time scale, such
      as the change from standard time to daylight time and back, the
      computation of the exact duration requires the substraction or
      addition of the change of duration of the discontinuity.  Leap

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      seconds MUST NOT be considered when computing an exact duration.
      When computing an exact duration, the greatest order time
      components MUST be added first, that is, the number of days MUST
      be added first, followed by the number of hours, number of
      minutes, and number of seconds.

      Negative durations are typically used to schedule an alarm to
      trigger before an associated time (see Section 3.8.6.3).

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) are defined for this value type.

   Example:  A duration of 15 days, 5 hours and 20 seconds would be:

        P15DT5H0M20S

      A duration of 7 weeks would be:

        P7W

3.3.7.  Float

   Value Name:  FLOAT

   Purpose:  This value type is used to identify properties that contain
      a real number value.

   Format Definition:  This value type is defined by the following
      notation:

        float      = (["+"] / "-") 1*DIGIT ["." 1*DIGIT]

   Description:  If the property permits, multiple "float" values are
      specified by a COMMA character (US-ASCII decimal 44) separated
      list of values.

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) is defined for this value type.

   Example:

        1000000.0000001
        1.333
        -3.14

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3.3.8.  Integer

   Value Name:  INTEGER

   Purpose:  This value type is used to identify properties that contain
      a signed integer value.

   Format Definition:  This value type is defined by the following
      notation:

        integer    = (["+"] / "-") 1*DIGIT

   Description:  If the property permits, multiple "integer" values are
      specified by a COMMA character (US-ASCII decimal 44) separated
      list of values.  The valid range for "integer" is -2147483648 to
      2147483647.  If the sign is not specified, then the value is
      assumed to be positive.

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) is defined for this value type.

   Example:

        1234567890
        -1234567890
        +1234567890
        432109876

3.3.9.  Period of Time

   Value Name:  PERIOD

   Purpose:  This value type is used to identify values that contain a
      precise period of time.

   Format Definition:  This value type is defined by the following
      notation:

        period     = period-explicit / period-start

        period-explicit = date-time "/" date-time
        ; [ISO.8601.2004] complete representation basic format for a
        ; period of time consisting of a start and end. The start MUST
        ; be before the end.

        period-start = date-time "/" dur-value
        ; [ISO.8601.2004] complete representation basic format for a
        ; period of time consisting of a start and positive duration

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        ; of time.

   Description:  If the property permits, multiple "period" values are
      specified by a COMMA character (US-ASCII decimal 44) separated
      list of values.  There are two forms of a period of time.  First,
      a period of time is identified by its start and its end.  This
      format is based on the [ISO.8601.2004] complete representation,
      basic format for "DATE-TIME" start of the period, followed by a
      SOLIDUS character (US-ASCII decimal 47), followed by the "DATE-
      TIME" of the end of the period.  The start of the period MUST be
      before the end of the period.  Second, a period of time can also
      be defined by a start and a positive duration of time.  The format
      is based on the [ISO.8601.2004] complete representation, basic
      format for the "DATE-TIME" start of the period, followed by a
      SOLIDUS character (US-ASCII decimal 47), followed by the
      [ISO.8601.2004] basic format for "DURATION" of the period.

   Example:  The period starting at 18:00:00 UTC, on January 1, 1997 and
      ending at 07:00:00 UTC on January 2, 1997 would be:

        19970101T180000Z/19970102T070000Z

      The period start at 18:00:00 on January 1, 1997 and lasting 5
      hours and 30 minutes would be:

        19970101T180000Z/PT5H30M

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) is defined for this value type.

3.3.10.  Recurrence Rule

   Value Name:  RECUR

   Purpose:  This value type is used to identify properties that contain
      a recurrence rule specification.

   Format Definition:  This value type is defined by the following
      notation:

        recur           = recur-rule-part *( ";" recur-rule-part )
                        ;
                        ; The rule parts are not ordered in any
                        ; particular sequence
                        ;
                        ; The FREQ rule part is REQUIRED,
                        ; but MUST NOT occur more than once
                        ;

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                        ; The UNTIL or COUNT rule parts are OPTIONAL,
                        ; but they MUST NOT occur in the same 'recur'
                        ;
                        ; The other rule parts are OPTIONAL,
                        ; but MUST NOT occur more than once

        recur-rule-part = ( "FREQ" "=" freq )
                        / ( "UNTIL" "=" enddate )
                        / ( "COUNT" "=" 1*DIGIT )
                        / ( "INTERVAL" "=" 1*DIGIT )
                        / ( "BYSECOND" "=" byseclist )
                        / ( "BYMINUTE" "=" byminlist )
                        / ( "BYHOUR" "=" byhrlist )
                        / ( "BYDAY" "=" bywdaylist )
                        / ( "BYMONTHDAY" "=" bymodaylist )
                        / ( "BYYEARDAY" "=" byyrdaylist )
                        / ( "BYWEEKNO" "=" bywknolist )
                        / ( "BYMONTH" "=" bymolist )
                        / ( "BYSETPOS" "=" bysplist )
                        / ( "WKST" "=" weekday )

        freq        = "SECONDLY" / "MINUTELY" / "HOURLY" / "DAILY"
                    / "WEEKLY" / "MONTHLY" / "YEARLY"

        enddate     = date / date-time

        byseclist   = ( seconds *("," seconds) )

        seconds     = 1*2DIGIT       ;0 to 60

        byminlist   = ( minutes *("," minutes) )

        minutes     = 1*2DIGIT       ;0 to 59

        byhrlist    = ( hour *("," hour) )

        hour        = 1*2DIGIT       ;0 to 23

        bywdaylist  = ( weekdaynum *("," weekdaynum) )

        weekdaynum  = [[plus / minus] ordwk] weekday

        plus        = "+"

        minus       = "-"

        ordwk       = 1*2DIGIT       ;1 to 53

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        weekday     = "SU" / "MO" / "TU" / "WE" / "TH" / "FR" / "SA"
        ;Corresponding to SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY,
        ;FRIDAY, and SATURDAY days of the week.

        bymodaylist = ( monthdaynum *("," monthdaynum) )

        monthdaynum = [plus / minus] ordmoday

        ordmoday    = 1*2DIGIT       ;1 to 31

        byyrdaylist = ( yeardaynum *("," yeardaynum) )

        yeardaynum  = [plus / minus] ordyrday

        ordyrday    = 1*3DIGIT      ;1 to 366

        bywknolist  = ( weeknum *("," weeknum) )

        weeknum     = [plus / minus] ordwk

        bymolist    = ( monthnum *("," monthnum) )

        monthnum    = 1*2DIGIT       ;1 to 12

        bysplist    = ( setposday *("," setposday) )

        setposday   = yeardaynum

   Description:  This value type is a structured value consisting of a
      list of one or more recurrence grammar parts.  Each rule part is
      defined by a NAME=VALUE pair.  The rule parts are separated from
      each other by the SEMICOLON character (US-ASCII decimal 59).  The
      rule parts are not ordered in any particular sequence.  Individual
      rule parts MUST only be specified once.  Compliant applications
      MUST accept rule parts ordered in any sequence, but to ensure
      backward compatibility with applications that pre-date this
      revision of iCalendar the FREQ rule part MUST be the first rule
      part specified in a RECUR value.

      The FREQ rule part identifies the type of recurrence rule.  This
      rule part MUST be specified in the recurrence rule.  Valid values
      include SECONDLY, to specify repeating events based on an interval
      of a second or more; MINUTELY, to specify repeating events based
      on an interval of a minute or more; HOURLY, to specify repeating
      events based on an interval of an hour or more; DAILY, to specify
      repeating events based on an interval of a day or more; WEEKLY, to
      specify repeating events based on an interval of a week or more;
      MONTHLY, to specify repeating events based on an interval of a

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      month or more; and YEARLY, to specify repeating events based on an
      interval of a year or more.

      The INTERVAL rule part contains a positive integer representing at
      which intervals the recurrence rule repeats.  The default value is
      "1", meaning every second for a SECONDLY rule, every minute for a
      MINUTELY rule, every hour for an HOURLY rule, every day for a
      DAILY rule, every week for a WEEKLY rule, every month for a
      MONTHLY rule, and every year for a YEARLY rule.  For example,
      within a DAILY rule, a value of "8" means every eight days.

      The UNTIL rule part defines a DATE or DATE-TIME value which bounds
      the recurrence rule in an inclusive manner.  If the value
      specified by UNTIL is synchronized with the specified recurrence,
      this DATE or DATE-TIME becomes the last instance of the
      recurrence.  The value of the UNTIL rule part MUST have the same
      value type as the "DTSTART" property.  Furthermore, if the
      "DTSTART" property is specified as a date with local time, then
      the UNTIL rule part MUST also be specified as a date with local
      time.  If the "DTSTART" property is specified as a date with UTC
      time or a date with local time and time zone reference, then the
      UNTIL rule part MUST be specified as a date with UTC time.  In the
      case of the "STANDARD" and "DAYLIGHT" sub-components the UNTIL
      rule part MUST always be specified as a date with UTC time.  If
      specified as a DATE-TIME value, then it MUST be specified in a UTC
      time format.  If not present, and the COUNT rule part is also not
      present, the "RRULE" is considered to repeat forever.

      The COUNT rule part defines the number of occurrences at which to
      range-bound the recurrence.  The "DTSTART" property value always
      counts as the first occurrence.

      The BYSECOND rule part specifies a COMMA character (US-ASCII
      decimal 44) separated list of seconds within a minute.  Valid
      values are 0 to 60.  The BYMINUTE rule part specifies a COMMA
      character (US-ASCII decimal 44) separated list of minutes within
      an hour.  Valid values are 0 to 59.  The BYHOUR rule part
      specifies a COMMA character (US-ASCII decimal 44) separated list
      of hours of the day.  Valid values are 0 to 23.  The BYSECOND,
      BYMINUTE and BYHOUR rule parts MUST NOT be specified when the
      associated "DTSTART" property has a DATE value type.  These rule
      parts MUST be ignored in RECUR value that violate the above
      requirement (e.g., generated by applications that pre-date this
      revision of iCalendar).

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      The BYDAY rule part specifies a COMMA character (US-ASCII decimal
      44) separated list of days of the week; SU indicates Sunday; MO
      indicates Monday; TU indicates Tuesday; WE indicates Wednesday; TH
      indicates Thursday; FR indicates Friday; SA indicates Saturday.

      Each BYDAY value can also be preceded by a positive (+n) or
      negative (-n) integer.  If present, this indicates the nth
      occurrence of a specific day within the MONTHLY or YEARLY "RRULE".
      For example, within a MONTHLY rule, +1MO (or simply 1MO)
      represents the first Monday within the month, whereas -1MO
      represents the last Monday of the month.  The numeric value in a
      BYDAY rule part with the FREQ rule part set to YEARLY corresponds
      to an offset within the month when the BYMONTH rule part is
      present, and corresponds to an offset within the year when the
      BYWEEKNO or BYMONTH rule parts are present.  If an integer
      modifier is not present, it means all days of this type within the
      specified frequency.  For example, within a MONTHLY rule, MO
      represents all Mondays within the month.  The BYDAY rule part MUST
      NOT be specified with a numeric value when the FREQ rule part is
      not set to MONTHLY or YEARLY.  Furthermore, the BYDAY rule part
      MUST NOT be specified with a numeric value with the FREQ rule part
      set to YEARLY when the BYWEEKNO rule part is specified.

      The BYMONTHDAY rule part specifies a COMMA character (US-ASCII
      decimal 44) separated list of days of the month.  Valid values are
      1 to 31 or -31 to -1.  For example, -10 represents the tenth to
      the last day of the month.  The BYMONTHDAY rule part MUST NOT be
      specified when the FREQ rule part is set to WEEKLY.

      The BYYEARDAY rule part specifies a COMMA character (US-ASCII
      decimal 44) separated list of days of the year.  Valid values are
      1 to 366 or -366 to -1.  For example, -1 represents the last day
      of the year (December 31st) and -306 represents the 306th to the
      last day of the year (March 1st).  The BYYEARDAY rule part MUST
      NOT be specified when the FREQ rule part is set to DAILY, WEEKLY,
      or MONTHLY.

      The BYWEEKNO rule part specifies a COMMA character (US-ASCII
      decimal 44) separated list of ordinals specifying weeks of the
      year.  Valid values are 1 to 53 or -53 to -1.  This corresponds to
      weeks according to week numbering as defined in [ISO.8601.2004].
      A week is defined as a seven day period, starting on the day of
      the week defined to be the week start (see WKST).  Week number one
      of the calendar year is the first week which contains at least
      four (4) days in that calendar year.  This rule part MUST NOT be
      used when the FREQ rule part is set to anything other than YEARLY.
      For example, 3 represents the third week of the year.

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         Note: Assuming a Monday week start, week 53 can only occur when
         Thursday is January 1 or if it is a leap year and Wednesday is
         January 1.

      The BYMONTH rule part specifies a COMMA character (US-ASCII
      decimal 44) separated list of months of the year.  Valid values
      are 1 to 12.

      The WKST rule part specifies the day on which the workweek starts.
      Valid values are MO, TU, WE, TH, FR, SA and SU.  This is
      significant when a WEEKLY "RRULE" has an interval greater than 1,
      and a BYDAY rule part is specified.  This is also significant when
      in a YEARLY "RRULE" when a BYWEEKNO rule part is specified.  The
      default value is MO.

      The BYSETPOS rule part specifies a COMMA character (US-ASCII
      decimal 44) separated list of values which corresponds to the nth
      occurrence within the set of recurrence instances specified by the
      rule.  BYSETPOS operates on a set of recurrence instances in one
      interval of the recurrence rule.  For example, in a WEEKLY rule,
      the interval would be one week A set of recurrence instances
      starts at the beginning of the interval defined by the FREQ rule
      part.  Valid values are 1 to 366 or -366 to -1.  It MUST only be
      used in conjunction with another BYxxx rule part.  For example
      "the last work day of the month" could be represented as:

        FREQ=MONTHLY;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=-1

      Each BYSETPOS value can include a positive (+n) or negative (-n)
      integer.  If present, this indicates the nth occurrence of the
      specific occurrence within the set of occurences specified by the
      rule.

      Recurrence rules may generate recurrence instances with invalid
      date (e.g., February 30) or nonexistent local time (e.g., 1:30 AM
      on a day where the local time is moved forward by an hour at 1:00
      AM).  Such recurrence instances MUST be ignored and MUST NOT be
      counted as part of the recurrence set.

      Information, not contained in the rule, necessary to determine the
      various recurrence instance start time and dates are derived from
      the Start Time ("DTSTART") component attribute.  For example,
      "FREQ=YEARLY;BYMONTH=1" doesn't specify a specific day within the
      month or a time.  This information would be the same as what is
      specified for "DTSTART".

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      BYxxx rule parts modify the recurrence in some manner.  BYxxx rule
      parts for a period of time which is the same or greater than the
      frequency generally reduce or limit the number of occurrences of
      the recurrence generated.  For example, "FREQ=DAILY;BYMONTH=1"
      reduces the number of recurrence instances from all days (if
      BYMONTH rule part is not present) to all days in January.  BYxxx
      rule parts for a period of time less than the frequency generally
      increase or expand the number of occurrences of the recurrence.
      For example, "FREQ=YEARLY;BYMONTH=1,2" increases the number of
      days within the yearly recurrence set from 1 (if BYMONTH rule part
      is not present) to 2.

      If multiple BYxxx rule parts are specified, then after evaluating
      the specified FREQ and INTERVAL rule parts, the BYxxx rule parts
      are applied to the current set of evaluated occurrences in the
      following order: BYMONTH, BYWEEKNO, BYYEARDAY, BYMONTHDAY, BYDAY,
      BYHOUR, BYMINUTE, BYSECOND and BYSETPOS; then COUNT and UNTIL are
      evaluated.

      The table below summarizes the dependency of BYxxx rule part
      expand or limit behaviour on the FREQ rule part value.

      The term "N/A" means that the corresponding BYxxx rule part MUST
      NOT be used with the corresponding FREQ value.

      BYDAY has some special behaviour depending on the FREQ value and
      this is described in separate notes below the table.

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   +----------+--------+--------+-------+-------+------+-------+------+
   |          |SECONDLY|MINUTELY|HOURLY |DAILY  |WEEKLY|MONTHLY|YEARLY|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYMONTH   |Limit   |Limit   |Limit  |Limit  |Limit |Limit  |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYWEEKNO  |N/A     |N/A     |N/A    |N/A    |N/A   |N/A    |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYYEARDAY |Limit   |Limit   |Limit  |N/A    |N/A   |N/A    |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYMONTHDAY|Limit   |Limit   |Limit  |Limit  |N/A   |Expand |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYDAY     |Limit   |Limit   |Limit  |Limit  |Expand|Note 1 |Note 2|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYHOUR    |Limit   |Limit   |Limit  |Expand |Expand|Expand |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYMINUTE  |Limit   |Limit   |Expand |Expand |Expand|Expand |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYSECOND  |Limit   |Expand  |Expand |Expand |Expand|Expand |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYSETPOS  |Limit   |Limit   |Limit  |Limit  |Limit |Limit  |Limit |
   +----------+--------+--------+-------+-------+------+-------+------+

      Note 1:  Limit if BYMONTHDAY is present, otherwise special expand
            for MONTHLY.

      Note 2:  Limit if BYYEARDAY or BYMONTHDAY is present, otherwise
            special expand for WEEKLY if BYWEEKNO present, otherwise
            special expand for MONTHLY if BYMONTH present, otherwise
            special expand for YEARLY.

      Here is an example of evaluating multiple BYxxx rule parts.

        DTSTART;TZID=America/New_York:19970105T083000
        RRULE:FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;
         BYMINUTE=30

      First, the "INTERVAL=2" would be applied to "FREQ=YEARLY" to
      arrive at "every other year".  Then, "BYMONTH=1" would be applied
      to arrive at "every January, every other year".  Then, "BYDAY=SU"
      would be applied to arrive at "every Sunday in January, every
      other year".  Then, "BYHOUR=8,9" would be applied to arrive at
      "every Sunday in January at 8 AM and 9 AM, every other year".
      Then, "BYMINUTE=30" would be applied to arrive at "every Sunday in
      January at 8:30 AM and 9:30 AM, every other year".  Then, lacking
      information from "RRULE", the second is derived from "DTSTART", to
      end up in "every Sunday in January at 8:30:00 AM and 9:30:00 AM,

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      every other year".  Similarly, if the BYMINUTE, BYHOUR, BYDAY,
      BYMONTHDAY or BYMONTH rule part were missing, the appropriate
      minute, hour, day or month would have been retrieved from the
      "DTSTART" property.

      If the computed local start time of a recurrence instance does not
      exist, or occurs more than once, for the specified time zone, the
      time of the recurrence instance is interpreted in the same manner
      as an explicit DATE-TIME value describing that date and time, as
      specified in Section 3.3.5.

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) is defined for this value type.

   Example:  The following is a rule which specifies 10 occurences which
      occur every other day:

        FREQ=DAILY;COUNT=10;INTERVAL=2

      There are other examples specified in Section 3.8.5.3.

3.3.11.  Text

   Value Name:  TEXT

   Purpose:  This value type is used to identify values that contain
      human readable text.

   Format Definition:  This value type is defined by the following
      notation.

        text       = *(TSAFE-CHAR / ":" / DQUOTE / ESCAPED-CHAR)
           ; Folded according to description above

        ESCAPED-CHAR = ("\\" / "\;" / "\," / "\N" / "\n")
           ; \\ encodes \, \N or \n encodes newline
           ; \; encodes ;, \, encodes ,

        TSAFE-CHAR = WSP / %x21 / %x23-2B / %x2D-39 / %x3C-5B /
                     %x5D-7E / NON-US-ASCII
           ; Any character except CONTROLs not needed by the current
           ; character set, DQUOTE, ";", ":", "\", ","

   Description:  If the property permits, multiple TEXT values are
      specified by a COMMA character (US-ASCII decimal 44) separated
      list of values.

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      The language in which the text is represented can be controlled by
      the "LANGUAGE" property parameter.

      An intentional formatted text line break MUST only be included in
      a "TEXT" property value by representing the line break with the
      character sequence of BACKSLASH (US-ASCII decimal 92), followed by
      a LATIN SMALL LETTER N (US-ASCII decimal 110) or a LATIN CAPITAL
      LETTER N (US-ASCII decimal 78), that is "\n" or "\N".

      The "TEXT" property values may also contain special characters
      that are used to signify delimiters, such as a COMMA character for
      lists of values or a SEMICOLON character for structured values.
      In order to support the inclusion of these special characters in
      "TEXT" property values, they MUST be escaped with a BACKSLASH
      character.  A BACKSLASH character (US-ASCII decimal 92) in a
      "TEXT" property value MUST be escaped with another BACKSLASH
      character.  A COMMA character in a "TEXT" property value MUST be
      escaped with a BACKSLASH character (US-ASCII decimal 92).  A
      SEMICOLON character in a "TEXT" property value MUST be escaped
      with a BACKSLASH character (US-ASCII decimal 92).  However, a
      COLON character in a "TEXT" property value SHALL NOT be escaped
      with a BACKSLASH character.

   Example:  A multiple line value of:

        Project XYZ Final Review
        Conference Room - 3B
        Come Prepared.

      would be represented as:

        Project XYZ Final Review\nConference Room - 3B\nCome Prepared.

3.3.12.  Time

   Value Name:  TIME

   Purpose:  This value type is used to identify values that contain a
      time of day.

   Format Definition:  This value type is defined by the following
      notation:

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        time         = time-hour time-minute time-second [time-utc]

        time-hour    = 2DIGIT        ;00-23
        time-minute  = 2DIGIT        ;00-59
        time-second  = 2DIGIT        ;00-60
        ;The "60" value is used to account for positive "leap" seconds.

        time-utc     = "Z"

   Description:  If the property permits, multiple "time" values are
      specified by a COMMA character (US-ASCII decimal 44) separated
      list of values.  No additional content value encoding (i.e.,
      BACKSLASH character encoding, see Section 3.3.11) is defined for
      this value type.

      The "TIME" value type is used to identify values that contain a
      time of day.  The format is based on the [ISO.8601.2004] complete
      representation, basic format for a time of day.  The text format
      consists of a two-digit 24-hour of the day (i.e., values 00-23),
      two-digit minute in the hour (i.e., values 00-59), and two-digit
      seconds in the minute (i.e., values 00-60).  The seconds value of
      60 MUST only be used to account for positive "leap" seconds.
      Fractions of a second are not supported by this format.

      In parallel to the "DATE-TIME" definition above, the "TIME" value
      type expresses time values in three forms:

      The form of time with UTC offset MUST NOT be used.  For example,
      the following is not valid for a time value:

        230000-0800        ;Invalid time format

      FORM #1 LOCAL TIME

      The local time form is simply a time value that does not contain
      the UTC designator nor does it reference a time zone.  For
      example, 11:00 PM:

        230000

      Time values of this type are said to be "floating" and are not
      bound to any time zone in particular.  They are used to represent
      the same hour, minute, and second value regardless of which time
      zone is currently being observed.  For example, an event can be
      defined that indicates that an individual will be busy from 11:00
      AM to 1:00 PM every day, no matter which time zone the person is
      in.  In these cases, a local time can be specified.  The recipient
      of an iCalendar object with a property value consisting of a local

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      time, without any relative time zone information, SHOULD interpret
      the value as being fixed to whatever time zone the "ATTENDEE" is
      in at any given moment.  This means that two "Attendees", may
      participate in the same event at different UTC times; floating
      time SHOULD only be used where that is reasonable behavior.

      In most cases, a fixed time is desired.  To properly communicate a
      fixed time in a property value, either UTC time or local time with
      time zone reference MUST be specified.

      The use of local time in a TIME value without the "TZID" property
      parameter is to be interpreted as floating time, regardless of the
      existence of "VTIMEZONE" calendar components in the iCalendar
      object.

      FORM #2: UTC TIME

      UTC time, or absolute time, is identified by a LATIN CAPITAL
      LETTER Z suffix character (US-ASCII decimal 90), the UTC
      designator, appended to the time value.  For example, the
      following represents 07:00 AM UTC:

        070000Z

      The "TZID" property parameter MUST NOT be applied to TIME
      properties whose time values are specified in UTC.

      FORM #3: LOCAL TIME AND TIME ZONE REFERENCE

      The local time with reference to time zone information form is
      identified by the use the "TZID" property parameter to reference
      the appropriate time zone definition.  "TZID" is discussed in
      detail in Section 3.2.19.

   Example:  The following represents 8:30 AM in New York in Winter,
      five hours behind UTC, in each of the three formats:

        083000
        133000Z

        TZID=America/New_York:083000

3.3.13.  URI

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   Value Name:  URI

   Purpose:  This value type is used to identify values that contain a
      uniform resource identifier (URI) type of reference to the
      property value.

   Format Definition:  This value type is defined by the following
      notation:

        uri = <As defined in section 3 of [RFC3986]>

   Description:  This value type might be used to reference binary
      information, for values that are large, or otherwise undesirable
      to include directly in the iCalendar object.

      Property values with this value type MUST follow the generic URI
      syntax defined in [RFC3986].

      When a property parameter value is a URI value type, the URI MUST
      be specified as a quoted-string value.

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) is defined for this value type.

   Example:  The following is a URI for a network file:

        http://example.com/my-report.txt

3.3.14.  UTC Offset

   Value Name:  UTC-OFFSET

   Purpose:  This value type is used to identify properties that contain
      an offset from UTC to local time.

   Format Definition:  This value type is defined by the following
      notation:

        utc-offset = time-numzone

        time-numzone = ("+" / "-") time-hour time-minute [time-second]

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   Description:  The PLUS SIGN (US-ASCII decimal 43) character MUST be
      specified for positive UTC offsets (i.e., ahead of UTC).  The
      HYPHEN-MINUS character (US-ASCII decimal 45) MUST be specified for
      negative UTC offsets (i.e., behind of UTC).  The value of "-0000"
      and "-000000" are not allowed.  The time-second, if present, MUST
      NOT be 60; if absent, it defaults to zero.

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) is defined for this value type.

   Example:  The following UTC offsets are given for standard time for
      New York (five hours behind UTC) and Geneva (one hour ahead of
      UTC):

        -0500

        +0100

3.4.  iCalendar Object

   The Calendaring and Scheduling Core Object is a collection of
   calendaring and scheduling information.  Typically, this information
   will consist of an iCalendar stream with a single iCalendar object.
   However, multiple iCalendar objects can be sequentially grouped
   together in an iCalendar stream.  The first line and last line of the
   iCalendar object MUST contain a pair of iCalendar object delimiter
   strings.  The syntax for an iCalendar stream is as follows:

        icalstream = 1*icalobject

        icalobject = "BEGIN" ":" "VCALENDAR" CRLF
                     icalbody
                     "END" ":" "VCALENDAR" CRLF

   The following is a simple example of an iCalendar object:

        BEGIN:VCALENDAR
        VERSION:2.0
        PRODID:-//hacksw/handcal//NONSGML v1.0//EN
        BEGIN:VEVENT
        UID:19970610T172345Z-AF23B2@example.com
        DTSTAMP:19970610T172345Z
        DTSTART:19970714T170000Z
        DTEND:19970715T040000Z
        SUMMARY:Bastille Day Party
        END:VEVENT
        END:VCALENDAR

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3.5.  Property

   A property is the definition of an individual attribute describing a
   calendar object or a calendar component.  A property takes the form
   defined by the "contentline" notation defined in Section 3.1.

   The following is an example of a property:

        DTSTART:19960415T133000Z

   This memo imposes no ordering of properties within an iCalendar
   object.

   Property names, parameter names and enumerated parameter values are
   case insensitive.  For example, the property name "DUE" is the same
   as "due" and "Due", DTSTART;TZID=America/New_York:19980714T120000 is
   the same as DtStart;TzID=America/New_York:19980714T120000.

3.6.  Calendar Components

   The body of the iCalendar object consists of a sequence of calendar
   properties and one or more calendar components.  The calendar
   properties are attributes that apply to the calendar object as a
   whole.  The calendar components are collections of properties that
   express a particular calendar semantic.  For example, the calendar
   component can specify an event, a to-do, a journal entry, time zone
   information, free/busy time information, or an alarm.

   The body of the iCalendar object is defined by the following
   notation:

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        icalbody   = calprops component

        calprops   = *(
                   ;
                   ; the following are REQUIRED,
                   ; but MUST NOT occur more than once
                   ;
                   prodid / version /
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   calscale / method /
                   ;
                   ; the following are OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   x-prop / iana-prop
                   ;
                   )

        component  = 1*(eventc / todoc / journalc / freebusyc /
                     timezonec / iana-comp / x-comp)

        iana-comp  = "BEGIN" ":" iana-token CRLF
                     1*contentline
                     "END" ":" iana-token CRLF

        x-comp     = "BEGIN" ":" x-name CRLF
                     1*contentline
                     "END" ":" x-name CRLF

   An iCalendar object MUST include the "PRODID" and "VERSION" calendar
   properties.  In addition, it MUST include at least one calendar
   component.  Special forms of iCalendar objects are possible to
   publish just busy time (i.e., only a "VFREEBUSY" calendar component)
   or time zone (i.e., only a "VTIMEZONE" calendar component)
   information.  In addition, a complex iCalendar object that is used to
   capture a complete snapshot of the contents of a calendar is possible
   (e.g., composite of many different calendar components).  More
   commonly, an iCalendar object will consist of just a single "VEVENT",
   "VTODO" or "VJOURNAL" calendar component.  Applications MUST ignore
   x-comp and iana-comp they don't recognized.  Applications that
   support importing iCalendar objects SHOULD support all of the
   component types defined in this document, and SHOULD NOT silently
   drop any components as that can lead to user data loss.

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3.6.1.  Event Component

   Component Name:  VEVENT

   Purpose:  Provide a grouping of component properties that describe an
      event.

   Format Definition:  A "VEVENT" calendar component is defined by the
      following notation:

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        eventc     = "BEGIN" ":" "VEVENT" CRLF
                     eventprop *alarmc
                     "END" ":" "VEVENT" CRLF

        eventprop  = *(
                   ;
                   ; the following are REQUIRED,
                   ; but MUST NOT occur more than once
                   ;
                   dtstamp / uid /
                   ;
                   ; the following is REQUIRED if the component
                   ; appears in an iCalendar object that doesn't
                   ; specify the "METHOD" property, otherwise it
                   ; is OPTIONAL, in any case it MUST NOT occur
                   ; more than once
                   ;
                   dtstart /
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   class / created / description / geo /
                   last-mod / location / organizer / priority /
                   seq / status / summary / transp /
                   url / recurid /
                   ;
                   ; the following is OPTIONAL,
                   ; but SHOULD NOT occur more than once
                   ;
                   rrule /
                   ;
                   ; either 'dtend' or 'duration' MAY appear in
                   ; a 'eventprop', but 'dtend' and 'duration'
                   ; MUST NOT occur in the same 'eventprop'
                   ;
                   dtend / duration /
                   ;
                   ; the following are OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   attach / attendee / categories / comment /
                   contact / exdate / rstatus / related /
                   resources / rdate / x-prop / iana-prop
                   ;
                   )

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   Description:  A "VEVENT" calendar component is a grouping of
      component properties, and possibly including "VALARM" calendar
      components, that represents a scheduled amount of time on a
      calendar.  For example, it can be an activity; such as a one-hour
      long, department meeting from 8:00 AM to 9:00 AM, tomorrow.
      Generally, an event will take up time on an individual calendar.
      Hence, the event will appear as an opaque interval in a search for
      busy time.  Alternately, the event can have its Time Transparency
      set to "TRANSPARENT" in order to prevent blocking of the event in
      searches for busy time.

      The "VEVENT" is also the calendar component used to specify an
      anniversary or daily reminder within a calendar.  These events
      have a DATE value type for the "DTSTART" property instead of the
      default value type of DATE-TIME.  If such a "VEVENT" has a "DTEND"
      property, it MUST be specified as a DATE value also.  The
      anniversary type of "VEVENT" can span more than one date (i.e.,
      "DTEND" property value is set to a calendar date after the
      "DTSTART" property value).  If such a "VEVENT" has a "DURATION"
      property, it MUST be specified as a "dur-day" or "dur-week" value.

      The "DTSTART" property for a "VEVENT" specifies the inclusive
      start of the event.  For recurring events, it also specifies the
      very first instance in the recurrence set.  The "DTEND" property
      for a "VEVENT" calendar component specifies the non-inclusive end
      of the event.  For cases where a "VEVENT" calendar component
      specifies a "DTSTART" property with a DATE value type but no
      "DTEND" nor "DURATION" property, the event's duration is taken to
      be one day.  For cases where a "VEVENT" calendar component
      specifies a "DTSTART" property with a DATE-TIME value type but no
      "DTEND" property, the event ends on the same calendar date and
      time of day specified by the "DTSTART" property.

      The "VEVENT" calendar component cannot be nested within another
      calendar component.  However, "VEVENT" calendar components can be
      related to each other or to a "VTODO" or to a "VJOURNAL" calendar
      component with the "RELATED-TO" property.

   Example:  The following is an example of the "VEVENT" calendar
      component used to represent a meeting that will also be opaque to
      searches for busy time:

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        BEGIN:VEVENT
        UID:19970901T130000Z-123401@example.com
        DTSTAMP:19970901T130000Z
        DTSTART:19970903T163000Z
        DTEND:19970903T190000Z
        SUMMARY:Annual Employee Review
        CLASS:PRIVATE
        CATEGORIES:BUSINESS,HUMAN RESOURCES
        END:VEVENT

      The following is an example of the "VEVENT" calendar component
      used to represent a reminder that will not be opaque, but rather
      transparent, to searches for busy time:

        BEGIN:VEVENT
        UID:19970901T130000Z-123402@example.com
        DTSTAMP:19970901T130000Z
        DTSTART:19970401T163000Z
        DTEND:19970402T010000Z
        SUMMARY:Laurel is in sensitivity awareness class.
        CLASS:PUBLIC
        CATEGORIES:BUSINESS,HUMAN RESOURCES
        TRANSP:TRANSPARENT
        END:VEVENT

      The following is an example of the "VEVENT" calendar component
      used to represent an anniversary that will occur annually.

        BEGIN:VEVENT
        UID:19970901T130000Z-123403@example.com
        DTSTAMP:19970901T130000Z
        DTSTART;VALUE=DATE:19971102
        SUMMARY:Our Blissful Anniversary
        TRANSP:TRANSPARENT
        CLASS:CONFIDENTIAL
        CATEGORIES:ANNIVERSARY,PERSONAL,SPECIAL OCCASION
        RRULE:FREQ=YEARLY
        END:VEVENT

      The following is an example of the "VEVENT" calendar component
      used to represent a multi-day event scheduled from June 28th, 2007
      to July 8th, 2007 inclusively.  Note that the "DTEND" property is
      set to July 9th, 2007, since the "DTEND" property specifies the
      non-inclusive end of the event.

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        BEGIN:VEVENT
        UID:20070423T123432Z-541111@example.com
        DTSTAMP:20070423T123432Z
        DTSTART;VALUE=DATE:20070628
        DTEND;VALUE=DATE:20070709
        SUMMARY:Festival International de Jazz de Montreal
        TRANSP:TRANSPARENT
        END:VEVENT

3.6.2.  To-do Component

   Component Name:  VTODO

   Purpose:  Provide a grouping of calendar properties that describe a
      to-do.

   Format Definition:  A "VTODO" calendar component is defined by the
      following notation:

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        todoc      = "BEGIN" ":" "VTODO" CRLF
                     todoprop *alarmc
                     "END" ":" "VTODO" CRLF

        todoprop   = *(
                   ;
                   ; the following are REQUIRED,
                   ; but MUST NOT occur more than once
                   ;
                   dtstamp / uid /
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   class / completed / created / description /
                   dtstart / geo / last-mod / location / organizer /
                   percent / priority / recurid / seq / status /
                   summary / url /
                   ;
                   ; the following is OPTIONAL,
                   ; but SHOULD NOT occur more than once
                   ;
                   rrule /
                   ;
                   ; either 'due' or 'duration' MAY appear in
                   ; a 'todoprop', but 'due' and 'duration'
                   ; MUST NOT occur in the same 'todoprop'.
                   ; If 'duration' appear in a 'todoprop',
                   ; then 'dtstart' MUST also appear in
                   ; the same 'todoprop'.
                   ;
                   due / duration /
                   ;
                   ; the following are OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   attach / attendee / categories / comment / contact /
                   exdate / rstatus / related / resources /
                   rdate / x-prop / iana-prop
                   ;
                   )

   Description:  A "VTODO" calendar component is a grouping of component
      properties and possibly "VALARM" calendar components that
      represent an action-item or assignment.  For example, it can be
      used to represent an item of work assigned to an individual; such
      as "turn in travel expense today".

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      The "VTODO" calendar component cannot be nested within another
      calendar component.  However, "VTODO" calendar components can be
      related to each other or to a "VEVENT" or to a "VJOURNAL" calendar
      component with the "RELATED-TO" property.

      A "VTODO" calendar component without the "DTSTART" and "DUE" (or
      "DURATION") properties specifies a to-do that will be associated
      with each successive calendar date, until it is completed.

   Examples:  The following is an example of a "VTODO" calendar
      component that needs to be completed before May 1st, 2007.  On
      midnight May 1st, 2007 this to-do would be considered overdue.

        BEGIN:VTODO
        UID:20070313T123432Z-456553@example.com
        DTSTAMP:20070313T123432Z
        DUE;VALUE=DATE:20070501
        SUMMARY:Submit Quebec Income Tax Return for 2006
        CLASS:CONFIDENTIAL
        CATEGORIES:FAMILY,FINANCE
        STATUS:NEEDS-ACTION
        END:VTODO

      The following is an example of a "VTODO" calendar component that
      was due before 1:00 P.M. UTC on July 9th, 2007 and was completed
      on July 7th, 2007 at 10:00 A.M. UTC.

        BEGIN:VTODO
        UID:20070514T103211Z-123404@example.com
        DTSTAMP:20070514T103211Z
        DTSTART:20070514T110000Z
        DUE:20070709T130000Z
        COMPLETED:20070707T100000Z
        SUMMARY:Submit Revised Internet-Draft
        PRIORITY:1
        STATUS:NEEDS-ACTION
        END:VTODO

3.6.3.  Journal Component

   Component Name:  VJOURNAL

   Purpose:  Provide a grouping of component properties that describe a
      journal entry.

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   Format Definition:  A "VJOURNAL" calendar component is defined by the
      following notation:

        journalc   = "BEGIN" ":" "VJOURNAL" CRLF
                     jourprop
                     "END" ":" "VJOURNAL" CRLF

        jourprop   = *(
                   ;
                   ; the following are REQUIRED,
                   ; but MUST NOT occur more than once
                   ;
                   dtstamp / uid /
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   class / created / dtstart /
                   last-mod / organizer / recurid / seq /
                   status / summary / url /
                   ;
                   ; the following is OPTIONAL,
                   ; but SHOULD NOT occur more than once
                   ;
                   rrule /
                   ;
                   ; the following are OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   attach / attendee / categories / comment /
                   contact / description / exdate / related / rdate /
                   rstatus / x-prop / iana-prop
                   ;
                   )

   Description:  A "VJOURNAL" calendar component is a grouping of
      component properties that represent one or more descriptive text
      notes associated with a particular calendar date.  The "DTSTART"
      property is used to specify the calendar date that the journal
      entry is associated with.  Generally, it will have a DATE value
      data type, but it can also be used to specify a DATE-TIME value
      data type.  Examples of a journal entry include a daily record of
      a legislative body or a journal entry of individual telephone
      contacts for the day or an ordered list of accomplishments for the
      day.  The "VJOURNAL" calendar component can also be used to
      associate a document with a calendar date.

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      The "VJOURNAL" calendar component does not take up time on a
      calendar.  Hence, it does not play a role in free or busy time
      searches -- it is as though it has a time transparency value of
      TRANSPARENT.  It is transparent to any such searches.

      The "VJOURNAL" calendar component cannot be nested within another
      calendar component.  However, "VJOURNAL" calendar components can
      be related to each other or to a "VEVENT" or to a "VTODO" calendar
      component, with the "RELATED-TO" property.

   Example:  The following is an example of the "VJOURNAL" calendar
      component:

        BEGIN:VJOURNAL
        UID:19970901T130000Z-123405@example.com
        DTSTAMP:19970901T130000Z
        DTSTART;VALUE=DATE:19970317
        SUMMARY:Staff meeting minutes
        DESCRIPTION:1. Staff meeting: Participants include Joe\, Lisa
          and Bob. Aurora project plans were reviewed. There is currentl
         y no budget reserves for this project. Lisa will escalate to
          management. Next meeting on Tuesday.\n
          2. Telephone Conference: ABC Corp. sales representative called
          to discuss new printer. Promised to get us a demo by Friday.\n
          3. Henry Miller (Handsoff Insurance): Car was totaled by tree.
          Is looking into a loaner car. 555-2323 (tel).
        END:VJOURNAL

3.6.4.  Free/Busy Component

   Component Name:  VFREEBUSY

   Purpose:  Provide a grouping of component properties that describe
      either a request for free/busy time, describe a response to a
      request for free/busy time or describe a published set of busy
      time.

   Format Definition:  A "VFREEBUSY" calendar component is defined by
      the following notation:

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        freebusyc  = "BEGIN" ":" "VFREEBUSY" CRLF
                     fbprop
                     "END" ":" "VFREEBUSY" CRLF

        fbprop     = *(
                   ;
                   ; the following are REQUIRED,
                   ; but MUST NOT occur more than once
                   ;
                   dtstamp / uid /
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   contact / dtstart / dtend /
                   organizer / url /
                   ;
                   ; the following are OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   attendee / comment / freebusy / rstatus / x-prop /
                   iana-prop
                   ;
                   )

   Description:  A "VFREEBUSY" calendar component is a grouping of
      component properties that represents either a request for, a reply
      to a request for free or busy time information or a published set
      of busy time information.

      When used to request free/busy time information, the "ATTENDEE"
      property specifies the calendar users whose free/busy time is
      being requested; the "ORGANIZER" property specifies the calendar
      user who is requesting the free/busy time; the "DTSTART" and
      "DTEND" properties specify the window of time for which the free/
      busy time is being requested; the "UID" and "DTSTAMP" properties
      are specified to assist in proper sequencing of multiple free/busy
      time requests.

      When used to reply to a request for free/busy time, the "ATTENDEE"
      property specifies the calendar user responding to the free/busy
      time request; the "ORGANIZER" property specifies the calendar user
      that originally requested the free/busy time; the "FREEBUSY"
      property specifies the free/busy time information (if it exists);
      and the "UID" and "DTSTAMP" properties are specified to assist in
      proper sequencing of multiple free/busy time replies.

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      When used to publish busy time, the "ORGANIZER" property specifies
      the calendar user associated with the published busy time; the
      "DTSTART" and "DTEND" properties specify an inclusive time window
      that surrounds the busy time information; the "FREEBUSY" property
      specifies the published busy time information; and the "DTSTAMP"
      property specifies the date/time that iCalendar object was
      created.

      The "VFREEBUSY" calendar component cannot be nested within another
      calendar component.  Multiple "VFREEBUSY" calendar components can
      be specified within an iCalendar object.  This permits the
      grouping of Free/Busy information into logical collections, such
      as monthly groups of busy time information.

      The "VFREEBUSY" calendar component is intended for use in
      iCalendar object methods involving requests for free time,
      requests for busy time, requests for both free and busy, and the
      associated replies.

      Free/Busy information is represented with the "FREEBUSY" property.
      This property provides a terse representation of time periods.
      One or more "FREEBUSY" properties can be specified in the
      "VFREEBUSY" calendar component.

      When present in a "VFREEBUSY" calendar component, the "DTSTART"
      and "DTEND" properties SHOULD be specified prior to any "FREEBUSY"
      properties.

      The recurrence properties ("RRULE", "RDATE", "EXDATE") are not
      permitted within a "VFREEBUSY" calendar component.  Any recurring
      events are resolved into their individual busy time periods using
      the "FREEBUSY" property.

   Example:  The following is an example of a "VFREEBUSY" calendar
      component used to request free or busy time information:

        BEGIN:VFREEBUSY
        UID:19970901T082949Z-FA43EF@example.com
        ORGANIZER:mailto:jane_doe@example.com
        ATTENDEE:mailto:john_public@example.com
        DTSTART:19971015T050000Z
        DTEND:19971016T050000Z
        DTSTAMP:19970901T083000Z
        END:VFREEBUSY

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      The following is an example of a "VFREEBUSY" calendar component
      used to reply to the request with busy time information:

        BEGIN:VFREEBUSY
        UID:19970901T095957Z-76A912@example.com
        ORGANIZER:mailto:jane_doe@example.com
        ATTENDEE:mailto:john_public@example.com
        DTSTAMP:19970901T100000Z
        FREEBUSY:19971015T050000Z/PT8H30M,
         19971015T160000Z/PT5H30M,19971015T223000Z/PT6H30M
        URL:http://example.com/pub/busy/jpublic-01.ifb
        COMMENT:This iCalendar file contains busy time information for
          the next three months.
        END:VFREEBUSY

      The following is an example of a "VFREEBUSY" calendar component
      used to publish busy time information.

        BEGIN:VFREEBUSY
        UID:19970901T115957Z-76A912@example.com
        DTSTAMP:19970901T120000Z
        ORGANIZER:jsmith@example.com
        DTSTART:19980313T141711Z
        DTEND:19980410T141711Z
        FREEBUSY:19980314T233000Z/19980315T003000Z
        FREEBUSY:19980316T153000Z/19980316T163000Z
        FREEBUSY:19980318T030000Z/19980318T040000Z
        URL:http://www.example.com/calendar/busytime/jsmith.ifb
        END:VFREEBUSY

3.6.5.  Time Zone Component

   Component Name:  VTIMEZONE

   Purpose:  Provide a grouping of component properties that defines a
      time zone.

   Format Definition:  A "VTIMEZONE" calendar component is defined by
      the following notation:

        timezonec  = "BEGIN" ":" "VTIMEZONE" CRLF
                     *(
                     ;
                     ; 'tzid' is REQUIRED, but MUST NOT occur more
                     ; than once
                     ;
                     tzid /
                     ;

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                     ; 'last-mod' and 'tzurl' are OPTIONAL,
                     ; but MUST NOT occur more than once
                     ;
                     last-mod / tzurl /
                     ;
                     ; one of 'standardc' or 'daylightc' MUST occur
                     ; and each MAY occur more than once.
                     ;
                     standardc / daylightc /
                     ;
                     ; the following are OPTIONAL,
                     ; and MAY occur more than once
                     ;
                     x-prop / iana-prop
                     ;
                     )
                     "END" ":" "VTIMEZONE" CRLF

        standardc  = "BEGIN" ":" "STANDARD" CRLF
                     tzprop
                     "END" ":" "STANDARD" CRLF

        daylightc  = "BEGIN" ":" "DAYLIGHT" CRLF
                     tzprop
                     "END" ":" "DAYLIGHT" CRLF

        tzprop     = *(
                     ;
                     ; the following are  REQUIRED,
                     ; but MUST NOT occur more than once
                     ;
                     dtstart / tzoffsetto / tzoffsetfrom /
                     ;
                     ; the following is OPTIONAL,
                     ; but SHOULD NOT occur more than once
                     ;
                     rrule /
                     ;
                     ; the following are OPTIONAL,
                     ; and MAY occur more than once
                     ;
                     comment / rdate / tzname / x-prop / iana-prop
                     ;
                     )

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   Description:  A time zone is unambiguously defined by the set of time
      measurement rules determined by the governing body for a given
      geographic area.  These rules describe at a minimum the base
      offset from UTC for the time zone, often referred to as the
      Standard Time offset.  Many locations adjust their Standard Time
      forward or backward by one hour, in order to accommodate seasonal
      changes in number of daylight hours, often referred to as Daylight
      Saving Time.  Some locations adjust their time by a fraction of an
      hour.  Standard Time is also known as Winter Time.  Daylight
      Saving Time is also known as Advanced Time, Summer Time, or Legal
      Time in certain countries.  The following table shows the changes
      in time zone rules in effect for New York City starting from 1967.
      Each line represents a description or rule for a particular
      observance.

                         Effective Observance Rule

     +-----------+--------------------------+--------+--------------+
     | Date      | (Date/Time)              | Offset | Abbreviation |
     +-----------+--------------------------+--------+--------------+
     | 1967-1973 | last Sun in Apr, 02:00   | -0400  | EDT          |
     |           |                          |        |              |
     | 1967-2006 | last Sun in Oct, 02:00   | -0500  | EST          |
     |           |                          |        |              |
     | 1974-1974 | Jan 6, 02:00             | -0400  | EDT          |
     |           |                          |        |              |
     | 1975-1975 | Feb 23, 02:00            | -0400  | EDT          |
     |           |                          |        |              |
     | 1976-1986 | last Sun in Apr, 02:00   | -0400  | EDT          |
     |           |                          |        |              |
     | 1987-2006 | first Sun in Apr, 02:00  | -0400  | EDT          |
     |           |                          |        |              |
     | 2007-*    | second Sun in Mar, 02:00 | -0400  | EDT          |
     |           |                          |        |              |
     | 2007-*    | first Sun in Nov, 02:00  | -0500  | EST          |
     +-----------+--------------------------+--------+--------------+

         Note: The specification of a global time zone registry is not
         addressed by this document and is left for future study.
         However, implementers may find the TZ database [TZDB] a useful
         reference.  It is an informal, public-domain collection of time
         zone information, which is currently being maintained by
         volunteer Internet participants, and is used in several
         operating systems.  This database contains current and
         historical time zone information for a wide variety of
         locations around the globe; it provides a time zone identifier
         for every unique time zone rule set in actual use since 1970,
         with historical data going back to the introduction of standard

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         time.

      Interoperability between two calendaring and scheduling
      applications, especially for recurring events, to-dos or journal
      entries, is dependent on the ability to capture and convey date
      and time information in an unambiguous format.  The specification
      of current time zone information is integral to this behavior.

      If present, the "VTIMEZONE" calendar component defines the set of
      Standard Time and Daylight Saving Time observances (or rules) for
      a particular time zone for a given interval of time.  The
      "VTIMEZONE" calendar component cannot be nested within other
      calendar components.  Multiple "VTIMEZONE" calendar components can
      exist in an iCalendar object.  In this situation, each "VTIMEZONE"
      MUST represent a unique time zone definition.  This is necessary
      for some classes of events, such as airline flights, that start in
      one time zone and end in another.

      The "VTIMEZONE" calendar component MUST include the "TZID"
      property and at least one definition of a "STANDARD" or "DAYLIGHT"
      sub-component.  The "STANDARD" or "DAYLIGHT" subcomponent MUST
      include the "DTSTART", "TZOFFSETFROM" and "TZOFFSETTO" properties.

      An individual "VTIMEZONE" calendar component MUST be specified for
      each unique "TZID" parameter value specified in the iCalendar
      object.  In addition, a "VTIMEZONE" calendar component, referred
      to by a recurring calendar component, MUST provide valid time zone
      information for all recurrence instances.

      Each "VTIMEZONE" calendar component consists of a collection of
      one or more sub-components that describe the rule for a particular
      observance (either a Standard Time or a Daylight Saving Time
      observance).  The "STANDARD" sub-component consists of a
      collection of properties that describe Standard Time.  The
      "DAYLIGHT" sub-component consists of a collection of properties
      that describe Daylight Saving Time.  In general this collection of
      properties consists of:

      *  the first onset date-time for the observance;

      *  the last onset date-time for the observance, if a last onset is
         known;

      *  the offset to be applied for the observance;

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      *  a rule that describes the day and time when the observance
         takes effect;

      *  an optional name for the observance.

      For a given time zone, there may be multiple unique definitions of
      the observances over a period of time.  Each observance is
      described using either a "STANDARD" or "DAYLIGHT" sub-component.
      The collection of these sub-components is used to describe the
      time zone for a given period of time.  The offset to apply at any
      given time is found by locating the observance that has the last
      onset date and time before the time in question, and using the
      offset value from that observance.

      The top-level properties in a "VTIMEZONE" calendar component are:

      The mandatory "TZID" property is a text value that uniquely
      identifies the "VTIMEZONE" calendar component within the scope of
      an iCalendar object.

      The optional "LAST-MODIFIED" property is a UTC value that
      specifies the date and time that this time zone definition was
      last updated.

      The optional "TZURL" property is a url value that points to a
      published "VTIMEZONE" definition.  "TZURL" SHOULD refer to a
      resource that is accessible by anyone who might need to interpret
      the object.  This SHOULD NOT normally be a "file" URL or other URL
      that is not widely-accessible.

      The collection of properties that are used to define the
      "STANDARD" and "DAYLIGHT" sub-components include:

      The mandatory "DTSTART" property gives the effective onset date
      and local time for the time zone sub-component definition.
      "DTSTART" in this usage MUST be specified as a date with local
      time value.

      The mandatory "TZOFFSETFROM" property gives the UTC offset which
      is in use when the onset of this time zone observance begins.
      "TZOFFSETFROM" is combined with "DTSTART" to define the effective
      onset for the time zone sub-component definition.  For example,
      the following represents the time at which the observance of
      Standard Time took effect in Fall 1967 for New York City:

        DTSTART:19671029T020000

        TZOFFSETFROM:-0400

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      The mandatory "TZOFFSETTO" property gives the UTC offset for the
      time zone sub-component (Standard Time or Daylight Saving Time)
      when this observance is in use.

      The optional "TZNAME" property is the customary name for the time
      zone.  This could be used for displaying dates.

      The onset date-times for the observance defined by the time zone
      sub-component is defined by the "DTSTART", "RRULE", and "RDATE"
      properties.

      The "RRULE" property defines the recurrence rule for the onset of
      the observance defined by this time zone sub-component.  Some
      specific requirements for the usage of "RRULE" for this purpose
      include:

      *  If observance is known to have an effective end date, the
         "UNTIL" recurrence rule parameter MUST be used to specify the
         last valid onset of this observance (i.e., the UNTIL date-time
         will be equal to the last instance generated by the recurrence
         pattern).  It MUST be specified in UTC time.

      *  The "DTSTART" and the "TZOFFSETFROM" properties MUST be used
         when generating the onset date-time values (instances) from the
         "RRULE".

      The "RDATE" property can also be used to define the onset of the
      observance by giving the individual onset date and times.  "RDATE"
      in this usage MUST be specified as a date with local time value,
      relative to the UTC offset specified in the "TZOFFSETFROM"
      property.

      The optional "COMMENT" property is also allowed for descriptive
      explanatory text.

   Example:  The following are examples of the "VTIMEZONE" calendar
      component:

      This is an example showing all the time zone rules for New York
      City since April 30, 1967 at 03:00:00 EDT.

        BEGIN:VTIMEZONE
        TZID:America/New_York
        LAST-MODIFIED:20050809T050000Z
        BEGIN:DAYLIGHT
        DTSTART:19670430T020000
        RRULE:FREQ=YEARLY;BYMONTH=4;BYDAY=-1SU;UNTIL=19730429T070000Z
        TZOFFSETFROM:-0500

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        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        BEGIN:STANDARD
        DTSTART:19671029T020000
        RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU;UNTIL=20061029T060000Z
        TZOFFSETFROM:-0400
        TZOFFSETTO:-0500
        TZNAME:EST
        END:STANDARD
        BEGIN:DAYLIGHT
        DTSTART:19740106T020000
        RDATE:19750223T020000
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        BEGIN:DAYLIGHT
        DTSTART:19760425T020000
        RRULE:FREQ=YEARLY;BYMONTH=4;BYDAY=-1SU;UNTIL=19860427T070000Z
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        BEGIN:DAYLIGHT
        DTSTART:19870405T020000
        RRULE:FREQ=YEARLY;BYMONTH=4;BYDAY=1SU;UNTIL=20060402T070000Z
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        BEGIN:DAYLIGHT
        DTSTART:20070311T020000
        RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        BEGIN:STANDARD
        DTSTART:20071104T020000
        RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
        TZOFFSETFROM:-0400
        TZOFFSETTO:-0500
        TZNAME:EST
        END:STANDARD
        END:VTIMEZONE

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      This is an example showing time zone information for New York City
      using only the "DTSTART" property.  Note that this is only
      suitable for a recurring event that starts on or later than March
      11, 2007 at 03:00:00 EDT (i.e., the earliest effective transition
      date and time) and ends no later than March 9, 2008 at 01:59:59
      EST (i.e., latest valid date and time for EST in this scenario).
      For example, this can be used for a recurring event that occurs
      every Friday, 8:00 A.M.-9:00 A.M., starting June 1, 2007, ending
      December 31, 2007,

        BEGIN:VTIMEZONE
        TZID:America/New_York
        LAST-MODIFIED:20050809T050000Z
        BEGIN:STANDARD
        DTSTART:20071104T020000
        TZOFFSETFROM:-0400
        TZOFFSETTO:-0500
        TZNAME:EST
        END:STANDARD
        BEGIN:DAYLIGHT
        DTSTART:20070311T020000
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        END:VTIMEZONE

      This is a simple example showing the current time zone rules for
      New York City using a "RRULE" recurrence pattern.  Note that there
      is no effective end date to either of the Standard Time or
      Daylight Time rules.  This information would be valid for a
      recurring event starting today and continuing indefinitely.

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        BEGIN:VTIMEZONE
        TZID:America/New_York
        LAST-MODIFIED:20050809T050000Z
        TZURL:http://zones.example.com/tz/America-New_York.ics
        BEGIN:STANDARD
        DTSTART:20071104T020000
        RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
        TZOFFSETFROM:-0400
        TZOFFSETTO:-0500
        TZNAME:EST
        END:STANDARD
        BEGIN:DAYLIGHT
        DTSTART:20070311T020000
        RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        END:VTIMEZONE

      This is an example showing a set of rules for a fictitious time
      zone where the Daylight Time rule has an effective end date (i.e.,
      after that date, Daylight Time is no longer observed).

        BEGIN:VTIMEZONE
        TZID:Fictitious
        LAST-MODIFIED:19870101T000000Z
        BEGIN:STANDARD
        DTSTART:19671029T020000
        RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
        TZOFFSETFROM:-0400
        TZOFFSETTO:-0500
        TZNAME:EST
        END:STANDARD
        BEGIN:DAYLIGHT
        DTSTART:19870405T020000
        RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4;UNTIL=19980404T070000Z
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        END:VTIMEZONE

      This is an example showing a set of rules for a fictitious time
      zone where the first Daylight Time rule has an effective end date.
      There is a second Daylight Time rule that picks up where the other
      left off.

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        BEGIN:VTIMEZONE
        TZID:Fictitious
        LAST-MODIFIED:19870101T000000Z
        BEGIN:STANDARD
        DTSTART:19671029T020000
        RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
        TZOFFSETFROM:-0400
        TZOFFSETTO:-0500
        TZNAME:EST
        END:STANDARD
        BEGIN:DAYLIGHT
        DTSTART:19870405T020000
        RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4;UNTIL=19980404T070000Z
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        BEGIN:DAYLIGHT
        DTSTART:19990424T020000
        RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=4
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        END:VTIMEZONE

3.6.6.  Alarm Component

   Component Name:  VALARM

   Purpose:  Provide a grouping of component properties that define an
      alarm.

   Format Definition:  A "VALARM" calendar component is defined by the
      following notation:

        alarmc     = "BEGIN" ":" "VALARM" CRLF
                     (audioprop / dispprop / emailprop)
                     "END" ":" "VALARM" CRLF

        audioprop  = *(
                   ;
                   ; 'action' and 'trigger' are both REQUIRED,
                   ; but MUST NOT occur more than once
                   ;
                   action / trigger /
                   ;
                   ; 'duration' and 'repeat' are both OPTIONAL,

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                   ; and MUST NOT occur more than once each,
                   ; but if one occurs, so MUST the other
                   ;
                   duration / repeat /
                   ;
                   ; the following is OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   attach /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   x-prop / iana-prop
                   ;
                   )

        dispprop   = *(
                   ;
                   ; the following are REQUIRED,
                   ; but MUST NOT occur more than once
                   ;
                   action / description / trigger /
                   ;
                   ; 'duration' and 'repeat' are both OPTIONAL,
                   ; and MUST NOT occur more than once each,
                   ; but if one occurs, so MUST the other
                   ;
                   duration / repeat /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   x-prop / iana-prop
                   ;
                   )

        emailprop  = *(
                   ;
                   ; the following are all REQUIRED,
                   ; but MUST NOT occur more than once
                   ;
                   action / description / trigger / summary /
                   ;
                   ; the following is REQUIRED,
                   ; and MAY occur more than once
                   ;
                   attendee /

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                   ;
                   ; 'duration' and 'repeat' are both OPTIONAL,
                   ; and MUST NOT occur more than once each,
                   ; but if one occurs, so MUST the other
                   ;
                   duration / repeat /
                   ;
                   ; the following are OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   attach / x-prop / iana-prop
                   ;
                   )

   Description:  A "VALARM" calendar component is a grouping of
      component properties that is a reminder or alarm for an event or a
      to-do.  For example, it may be used to define a reminder for a
      pending event or an overdue to-do.

      The "VALARM" calendar component MUST include the "ACTION" and
      "TRIGGER" properties.  The "ACTION" property further constrains
      the "VALARM" calendar component in the following ways:

      When the action is "AUDIO", the alarm can also include one and
      only one "ATTACH" property, which MUST point to a sound resource,
      which is rendered when the alarm is triggered.

      When the action is "DISPLAY", the alarm MUST also include a
      "DESCRIPTION" property, which contains the text to be displayed
      when the alarm is triggered.

      When the action is "EMAIL", the alarm MUST include a "DESCRIPTION"
      property, which contains the text to be used as the message body,
      a "SUMMARY" property, which contains the text to be used as the
      message subject, and one or more "ATTENDEE" properties, which
      contain the email address of attendees to receive the message.  It
      can also include one or more "ATTACH" properties, which are
      intended to be sent as message attachments.  When the alarm is
      triggered, the email message is sent.

      The "VALARM" calendar component MUST only appear within either a
      "VEVENT" or "VTODO" calendar component.  "VALARM" calendar
      components cannot be nested.  Multiple mutually independent
      "VALARM" calendar components can be specified for a single
      "VEVENT" or "VTODO" calendar component.

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      The "TRIGGER" property specifies when the alarm will be triggered.
      The "TRIGGER" property specifies a duration prior to the start of
      an event or a to-do.  The "TRIGGER" edge may be explicitly set to
      be relative to the "START" or "END" of the event or to-do with the
      "RELATED" parameter of the "TRIGGER" property.  The "TRIGGER"
      property value type can alternatively be set to an absolute
      calendar date with UTC time.

      In an alarm set to trigger on the "START" of an event or to-do,
      the "DTSTART" property MUST be present in the associated event or
      to-do.  In an alarm in a "VEVENT" calendar component set to
      trigger on the "END" of the event, either the "DTEND" property
      MUST be present, or the "DTSTART" and "DURATION" properties MUST
      both be present.  In an alarm in a "VTODO" calendar component set
      to trigger on the "END" of the to-do, either the "DUE" property
      MUST be present, or the "DTSTART" and "DURATION" properties MUST
      both be present.

      The alarm can be defined such that it triggers repeatedly.  A
      definition of an alarm with a repeating trigger MUST include both
      the "DURATION" and "REPEAT" properties.  The "DURATION" property
      specifies the delay period, after which the alarm will repeat.
      The "REPEAT" property specifies the number of additional
      repetitions that the alarm will be triggered.  This repetition
      count is in addition to the initial triggering of the alarm.  Both
      of these properties MUST be present in order to specify a
      repeating alarm.  If one of these two properties is absent, then
      the alarm will not repeat beyond the initial trigger.

      The "ACTION" property is used within the "VALARM" calendar
      component to specify the type of action invoked when the alarm is
      triggered.  The "VALARM" properties provide enough information for
      a specific action to be invoked.  It is typically the
      responsibility of a "Calendar User Agent" (CUA) to deliver the
      alarm in the specified fashion.  An "ACTION" property value of
      AUDIO specifies an alarm that causes a sound to be played to alert
      the user; DISPLAY specifies an alarm that causes a text message to
      be displayed to the user; and EMAIL specifies an alarm that causes
      an electronic email message to be delivered to one or more email
      addresses.

      In an AUDIO alarm, if the optional "ATTACH" property is included,
      it MUST specify an audio sound resource.  The intention is that
      the sound will be played as the alarm effect.  If an "ATTACH"
      property is specified that does not refer to a sound resource, or
      if the specified sound resource cannot be rendered (because its
      format is unsupported, or because it cannot be retrieved), then
      the CUA or other entity responsible for playing the sound may

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      choose a fallback action, such as playing a built-in default
      sound, or playing no sound at all.

      In a DISPLAY alarm, the intended alarm effect is for the text
      value of the "DESCRIPTION" property to be displayed to the user.

      In an EMAIL alarm, the intended alarm effect is for an email
      message to be composed and delivered to all the addresses
      specified by the "ATTENDEE" properties in the "VALARM" calendar
      component.  The "DESCRIPTION" property of the "VALARM" calendar
      component MUST be used as the body text of the message, and the
      "SUMMARY" property MUST be used as the subject text.  Any "ATTACH"
      properties in the "VALARM" calendar component SHOULD be sent as
      attachments to the message.

         Note: Implementations should carefully consider whether they
         accept alarm components from untrusted sources, e.g., when
         importing calendar objects from external sources.  One
         reasonable policy is to always ignore alarm components that the
         calendar user has not set herself, or at least ask for
         confirmation in such a case.

   Example:  The following example is for a "VALARM" calendar component
      that specifies an audio alarm that will sound at a precise time
      and repeat 4 more times at 15 minute intervals:

        BEGIN:VALARM
        TRIGGER;VALUE=DATE-TIME:19970317T133000Z
        REPEAT:4
        DURATION:PT15M
        ACTION:AUDIO
        ATTACH;FMTTYPE=audio/basic:ftp://example.com/pub/
         sounds/bell-01.aud
        END:VALARM

      The following example is for a "VALARM" calendar component that
      specifies a display alarm that will trigger 30 minutes before the
      scheduled start of the event or of the to-do it is associated with
      and will repeat 2 more times at 15 minute intervals:

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        BEGIN:VALARM
        TRIGGER:-PT30M
        REPEAT:2
        DURATION:PT15M
        ACTION:DISPLAY
        DESCRIPTION:Breakfast meeting with executive\n
         team at 8:30 AM EST.
        END:VALARM

      The following example is for a "VALARM" calendar component that
      specifies an email alarm that will trigger 2 days before the
      scheduled due date/time of a to-do it is associated with.  It does
      not repeat.  The email has a subject, body and attachment link.

        BEGIN:VALARM
        TRIGGER;RELATED=END:-P2D
        ACTION:EMAIL
        ATTENDEE:mailto:john_doe@example.com
        SUMMARY:*** REMINDER: SEND AGENDA FOR WEEKLY STAFF MEETING ***
        DESCRIPTION:A draft agenda needs to be sent out to the attendees
          to the weekly managers meeting (MGR-LIST). Attached is a
          pointer the document template for the agenda file.
        ATTACH;FMTTYPE=application/msword:http://example.com/
         templates/agenda.doc
        END:VALARM

3.7.  Calendar Properties

   The Calendar Properties are attributes that apply to the iCalendar
   object, as a whole.  These properties do not appear within a calendar
   component.  They SHOULD be specified after the "BEGIN:VCALENDAR"
   delimiter string and prior to any calendar component.

3.7.1.  Calendar Scale

   Property Name:  CALSCALE

   Purpose:  This property defines the calendar scale used for the
      calendar information specified in the iCalendar object.

   Value Type:  TEXT

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

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   Conformance:  This property can be specified once in an iCalendar
      object.  The default value is "GREGORIAN".

   Description:  This memo is based on the Gregorian calendar scale.
      The Gregorian calendar scale is assumed if this property is not
      specified in the iCalendar object.  It is expected that other
      calendar scales will be defined in other specifications or by
      future versions of this memo.

   Format Definition:  This property is defined by the following
      notation:

        calscale   = "CALSCALE" calparam ":" calvalue CRLF

        calparam   = *(";" other-param)

        calvalue   = "GREGORIAN"

   Example:  The following is an example of this property:

        CALSCALE:GREGORIAN

3.7.2.  Method

   Property Name:  METHOD

   Purpose:  This property defines the iCalendar object method
      associated with the calendar object.

   Value Type:  TEXT

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified once in an iCalendar
      object.

   Description:  When used in a MIME message entity, the value of this
      property MUST be the same as the Content-Type "method" parameter
      value.  If either the "METHOD" property or the Content-Type
      "method" parameter is specified, then the other MUST also be
      specified.

      No methods are defined by this specification.  This is the subject
      of other specifications, such as the iCalendar Transport-
      independent Interoperability Protocol (iTIP) defined by
      [I-D.ietf-calsify-2446bis].

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      If this property is not present in the iCalendar object, then a
      scheduling transaction MUST NOT be assumed.  In such cases, the
      iCalendar object is merely being used to transport a snapshot of
      some calendar information; without the intention of conveying a
      scheduling semantic.

   Format Definition:  This property is defined by the following
      notation:

        method     = "METHOD" metparam ":" metvalue CRLF

        metparam   = *(";" other-param)

        metvalue   = iana-token

   Example:  The following is a hypothetical example of this property to
      convey that the iCalendar object is a scheduling request:

        METHOD:REQUEST

3.7.3.  Product Identifier

   Property Name:  PRODID

   Purpose:  This property specifies the identifier for the product that
      created the iCalendar object.

   Value Type:  TEXT

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  The property MUST be specified once in an iCalendar
      object.

   Description:  The vendor of the implementation SHOULD assure that
      this is a globally unique identifier; using some technique such as
      an FPI value, as defined in [ISO.9070.1991].

      This property SHOULD NOT be used to alter the interpretation of an
      iCalendar object beyond the semantics specified in this memo.  For
      example, it is not to be used to further the understanding of non-
      standard properties.

   Format Definition:  This property is defined by the following
      notation:

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        prodid     = "PRODID" pidparam ":" pidvalue CRLF

        pidparam   = *(";" other-param)

        pidvalue   = text
        ;Any text that describes the product and version
        ;and that is generally assured of being unique.

   Example:  The following is an example of this property.  It does not
      imply that English is the default language.

        PRODID:-//ABC Corporation//NONSGML My Product//EN

3.7.4.  Version

   Property Name:  VERSION

   Purpose:  This property specifies the identifier corresponding to the
      highest version number or the minimum and maximum range of the
      iCalendar specification that is required in order to interpret the
      iCalendar object.

   Value Type:  TEXT

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property MUST be specified once in an iCalendar
      object.

   Description:  A value of "2.0" corresponds to this memo.

   Format Definition:  This property is defined by the following
      notation:

        version    = "VERSION" verparam ":" vervalue CRLF

        verparam   = *(";" other-param)

        vervalue   = "2.0"         ;This memo
                   / maxver
                   / (minver ";" maxver)

        minver     = <A IANA registered iCalendar version identifier>
        ;Minimum iCalendar version needed to parse the iCalendar object

        maxver     = <A IANA registered iCalendar version identifier>
        ;Maximum iCalendar version needed to parse the iCalendar object

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   Example:  The following is an example of this property:

        VERSION:2.0

3.8.  Component Properties

   The following properties can appear within calendar components, as
   specified by each component property definition.

3.8.1.  Descriptive Component Properties

   The following properties specify descriptive information about
   calendar components.

3.8.1.1.  Attachment

   Property Name:  ATTACH

   Purpose:  This property provides the capability to associate a
      document object with a calendar component.

   Value Type:  The default value type for this property is URI.  The
      value type can also be set to BINARY to indicate inline binary
      encoded content information.

   Property Parameters:  IANA, non-standard, inline encoding and value
      data type property parameters can be specified on this property.
      The format type parameter can be specified on this property and is
      RECOMMENDED for inline binary encoded content information.

   Conformance:  This property can be specified multiple times in a
      "VEVENT", "VTODO", "VJOURNAL" or "VALARM" calendar component with
      the exception of AUDIO alarm which only allows this property to
      occur once .

   Description:  This property is used in "VEVENT", "VTODO", and
      "VJOURNAL" calendar components to associate a resource (e.g.,
      document) with the calendar component.  This property is used in
      "VALARM" calendar components to specify an audio sound resource or
      an email message attachment.  This property can be specified as a
      URI pointing to a resource or as inline binary encoded content.

      When this property is specified as inline binary encoded content,
      calendar applications MAY attempt to guess the media type of the
      resource via inspection of its content if and only if the media
      type of the resource is not given by the "FMTTYPE" parameter.  If
      the media type remains unknown, calendar applications SHOULD treat
      it as type "application/octet-stream".

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   Format Definition:  This property is defined by the following
      notation:

        attach     = "ATTACH" attachparam ( ":" uri ) /
                     (
                       ";" "ENCODING" "=" "BASE64"
                       ";" "VALUE" "=" "BINARY"
                       ":" binary
                     )
                     CRLF

        attachparam = *(
                    ;
                    ; the following is OPTIONAL for URI value
                    ; and RECOMMENDED for BINARY value,
                    ; and MUST NOT occur more than once
                    ;
                    (";" fmttypeparam) /
                    ;
                    ; the following is OPTIONAL,
                    ; and MAY occur more than once
                    ;
                    (";" other-param)
                    ;
                    )

   Example:  The following are examples of this property:

        ATTACH:CID:jsmith.part3.960817T083000.xyzMail@example.com

        ATTACH;FMTTYPE=application/postscript:ftp://example.com/pub/
         reports/r-960812.ps

3.8.1.2.  Categories

   Property Name:  CATEGORIES

   Purpose:  This property defines the categories for a calendar
      component.

   Value Type:  TEXT

   Property Parameters:  IANA, non-standard, and language property
      parameters can be specified on this property.

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   Conformance:  The property can be specified within "VEVENT", "VTODO"
      or "VJOURNAL" calendar components.

   Description:  This property is used to specify categories or subtypes
      of the calendar component.  The categories are useful in searching
      for a calendar component of a particular type and category.
      Within the "VEVENT", "VTODO" or "VJOURNAL" calendar components,
      more than one category can be specified as a list of categories
      separated by the COMMA character (US-ASCII decimal 44).

   Format Definition:  This property is defined by the following
      notation:

        categories = "CATEGORIES" catparam ":" text *("," text)
                     CRLF

        catparam   = *(
                   ;
                   ; the following is OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" languageparam ) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

   Example:  The following are examples of this property:

        CATEGORIES:APPOINTMENT,EDUCATION

        CATEGORIES:MEETING

3.8.1.3.  Classification

   Property Name:  CLASS

   Purpose:  This property defines the access classification for a
      calendar component.

   Value Type:  TEXT

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   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  The property can be specified once in a "VEVENT",
      "VTODO" or "VJOURNAL" calendar components.

   Description:  An access classification is only one component of the
      general security system within a calendar application.  It
      provides a method of capturing the scope of the access the
      calendar owner intends for information within an individual
      calendar entry.  The access classification of an individual
      iCalendar component is useful when measured along with the other
      security components of a calendar system (e.g., calendar user
      authentication, authorization, access rights, access role, etc.).
      Hence, the semantics of the individual access classifications
      cannot be completely defined by this memo alone.  Additionally,
      due to the "blind" nature of most exchange processes using this
      memo, these access classifications cannot serve as an enforcement
      statement for a system receiving an iCalendar object.  Rather,
      they provide a method for capturing the intention of the calendar
      owner for the access to the calendar component.  If not specified
      in a component that allows this property, the default value is
      PUBLIC.  Applications MUST treat x-name and iana-token value they
      don't recognized the same way as they would the PRIVATE value.

   Format Definition:  This property is defined by the following
      notation:

        class      = "CLASS" classparam ":" classvalue CRLF

        classparam = *(";" other-param)

        classvalue = "PUBLIC" / "PRIVATE" / "CONFIDENTIAL" / iana-token
                   / x-name
        ;Default is PUBLIC

   Example:  The following is an example of this property:

        CLASS:PUBLIC

3.8.1.4.  Comment

   Property Name:  COMMENT

   Purpose:  This property specifies non-processing information intended
      to provide a comment to the calendar user.

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   Value Type:  TEXT

   Property Parameters:  IANA, non-standard, alternate text
      representation and language property parameters can be specified
      on this property.

   Conformance:  This property can be specified multiple times in
      "VEVENT", "VTODO", "VJOURNAL", and "VFREEBUSY" calendar components
      as well as in the "STANDARD" and "DAYLIGHT" sub-components.

   Description:  This property is used to specify a comment to the
      calendar user.

   Format Definition:  This property is defined by the following
      notation:

        comment    = "COMMENT" commparam ":" text CRLF

        commparam  = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" altrepparam) / (";" languageparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

   Example:  The following is an example of this property:

        COMMENT:The meeting really needs to include both ourselves
          and the customer. We can't hold this meeting without them.
          As a matter of fact\, the venue for the meeting ought to be at
          their site. - - John

3.8.1.5.  Description

   Property Name:  DESCRIPTION

   Purpose:  This property provides a more complete description of the
      calendar component, than that provided by the "SUMMARY" property.

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   Value Type:  TEXT

   Property Parameters:  IANA, non-standard, alternate text
      representation and language property parameters can be specified
      on this property.

   Conformance:  The property can be specified in the "VEVENT", "VTODO",
      "VJOURNAL" or "VALARM" calendar components.  The property can be
      specified multiple times only within a "VJOURNAL" calendar
      component.

   Description:  This property is used in the "VEVENT" and "VTODO" to
      capture lengthy textual decriptions associated with the activity.

      This property is used in the "VJOURNAL" calendar component to
      capture one or more textual journal entries.

      This property is used in the "VALARM" calendar component to
      capture the display text for a DISPLAY category of alarm, and to
      capture the body text for an EMAIL category of alarm.

   Format Definition:  This property is defined by the following
      notation:

        description        = "DESCRIPTION" descparam ":" text CRLF

        descparam  = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" altrepparam) / (";" languageparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

   Example:  The following is an example of this property with formatted
      line breaks in the property value:

        DESCRIPTION:Meeting to provide technical review for "Phoenix"
          design.\nHappy Face Conference Room. Phoenix design team
          MUST attend this meeting.\nRSVP to team leader.

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3.8.1.6.  Geographic Position

   Property Name:  GEO

   Purpose:  This property specifies information related to the global
      position for the activity specified by a calendar component.

   Value Type:  FLOAT.  The value MUST be two SEMICOLON separated FLOAT
      values.

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified in "VEVENT" or "VTODO"
      calendar components.

   Description:  This property value specifies latitude and longitude,
      in that order (i.e., "LAT LON" ordering).  The longitude
      represents the location East or West of the prime meridian as a
      positive or negative real number, respectively.  The longitude and
      latitude values MAY be specified up to six decimal places, which
      will allow for accuracy to within one meter of geographical
      position.  Receiving applications MUST accept values of this
      precision and MAY truncate values of greater precision.

      Values for latitude and longitude shall be expressed as decimal
      fractions of degrees.  Whole degrees of latitude shall be
      represented by a two-digit decimal number ranging from 0 through
      90.  Whole degrees of longitude shall be represented by a decimal
      number ranging from 0 through 180.  When a decimal fraction of a
      degree is specified, it shall be separated from the whole number
      of degrees by a decimal point.

      Latitudes North of the equator shall be specified by a plus sign
      (+), or by the absence of a minus sign (-), preceding the digits
      designating degrees.  Latitudes South of the Equator shall be
      designated by a minus sign (-) preceding the digits designating
      degrees.  A point on the Equator shall be assigned to the Northern
      Hemisphere.

      Longitudes east of the prime meridian shall be specified by a plus
      sign (+), or by the absence of a minus sign (-), preceding the
      digits designating degrees.  Longitudes west of the meridian shall
      be designated by minus sign (-) preceding the digits designating
      degrees.  A point on the prime meridian shall be assigned to the
      Eastern Hemisphere.  A point on the 180th meridian shall be
      assigned to the Western Hemisphere.  One exception to this last
      convention is permitted.  For the special condition of describing

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      a band of latitude around the earth, the East Bounding Coordinate
      data element shall be assigned the value +180 (180) degrees.

      Any spatial address with a latitude of +90 (90) or -90 degrees
      will specify the position at the North or South Pole,
      respectively.  The component for longitude may have any legal
      value.

      With the exception of the special condition described above, this
      form is specified in Department of Commerce, 1986, Representation
      of geographic point locations for information interchange (Federal
      Information Processing Standard 70-1): Washington, Department of
      Commerce, National Institute of Standards and Technology.

      The simple formula for converting degrees-minutes-seconds into
      decimal degrees is:

      decimal = degrees + minutes/60 + seconds/3600.

   Format Definition:  This property is defined by the following
      notation:

        geo        = "GEO" geoparam ":" geovalue CRLF

        geoparam   = *(";" other-param)

        geovalue   = float ";" float
        ;Latitude and Longitude components

   Example:  The following is an example of this property:

        GEO:37.386013;-122.082932

3.8.1.7.  Location

   Property Name:  LOCATION

   Purpose:  This property defines the intended venue for the activity
      defined by a calendar component.

   Value Type:  TEXT

   Property Parameters:  IANA, non-standard, alternate text
      representation and language property parameters can be specified
      on this property.

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   Conformance:  This property can be specified in "VEVENT" or "VTODO"
      calendar component.

   Description:  Specific venues such as conference or meeting rooms may
      be explicitly specified using this property.  An alternate
      representation may be specified that is a URI that points to
      directory information with more structured specification of the
      location.  For example, the alternate representation may specify
      either an LDAP URL [RFC4516] pointing to an LDAP server entry or a
      CID URL [RFC2392] pointing to a MIME body part containing a vCard
      [RFC2426] for the location.

   Format Definition:  This property is defined by the following
      notation:

        location   = "LOCATION"  locparam ":" text CRLF

        locparam   = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" altrepparam) / (";" languageparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

   Example:  The following are some examples of this property:

        LOCATION:Conference Room - F123\, Bldg. 002

        LOCATION;ALTREP="http://xyzcorp.com/conf-rooms/f123.vcf":
         Conference Room - F123\, Bldg. 002

3.8.1.8.  Percent Complete

   Property Name:  PERCENT-COMPLETE

   Purpose:  This property is used by an assignee or delegatee of a
      to-do to convey the percent completion of a to-do to the
      "Organizer".

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   Value Type:  INTEGER

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified once in a "VTODO"
      calendar component.

   Description:  The property value is a positive integer between zero
      and one hundred.  A value of "0" indicates the to-do has not yet
      been started.  A value of "100" indicates that the to-do has been
      completed.  Integer values in between indicate the percent
      partially complete.

      When a to-do is assigned to multiple individuals, the property
      value indicates the percent complete for that portion of the to-do
      assigned to the assignee or delegatee.  For example, if a to-do is
      assigned to both individuals "A" and "B".  A reply from "A" with a
      percent complete of "70" indicates that "A" has completed 70% of
      the to-do assigned to them.  A reply from "B" with a percent
      complete of "50" indicates "B" has completed 50% of the to-do
      assigned to them.

   Format Definition:  This property is defined by the following
      notation:

        percent = "PERCENT-COMPLETE" pctparam ":" integer CRLF

        pctparam   = *(";" other-param)

   Example:  The following is an example of this property to show 39%
      completion:

        PERCENT-COMPLETE:39

3.8.1.9.  Priority

   Property Name:  PRIORITY

   Purpose:  This property defines the relative priority for a calendar
      component.

   Value Type:  INTEGER

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

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   Conformance:  This property can be specified in "VEVENT" and "VTODO"
      calendar components.

   Description:  This priority is specified as an integer in the range
      zero to nine.  A value of zero (US-ASCII decimal 48) specifies an
      undefined priority.  A value of one (US-ASCII decimal 49) is the
      highest priority.  A value of two (US-ASCII decimal 50) is the
      second highest priority.  Subsequent numbers specify a decreasing
      ordinal priority.  A value of nine (US-ASCII decimal 57 ) is the
      lowest priority.

      A CUA with a three-level priority scheme of "HIGH", "MEDIUM" and
      "LOW" is mapped into this property such that a property value in
      the range of one (US-ASCII decimal 49) to four (US-ASCII decimal
      52) specifies "HIGH" priority.  A value of five (US-ASCII decimal
      53) is the normal or "MEDIUM" priority.  A value in the range of
      six (US-ASCII decimal 54) to nine (US-ASCII decimal 57 ) is "LOW"
      priority.

      A CUA with a priority schema of "A1", "A2", "A3", "B1", "B2", ...,
      "C3" is mapped into this property such that a property value of
      one (US-ASCII decimal 49) specifies "A1", a property value of two
      (US-ASCII decimal 50) specifies "A2", a property value of three
      (US-ASCII decimal 51) specifies "A3", and so forth up to a
      property value of 9 (US-ASCII decimal 57 ) specifies "C3".

      Other integer values are reserved for future use.

      Within a "VEVENT" calendar component, this property specifies a
      priority for the event.  This property may be useful when more
      than one event is scheduled for a given time period.

      Within a "VTODO" calendar component, this property specified a
      priority for the to-do.  This property is useful in prioritizing
      multiple action items for a given time period.

   Format Definition:  This property is defined by the following
      notation:

        priority   = "PRIORITY" prioparam ":" priovalue CRLF
        ;Default is zero (i.e., undefined)

        prioparam  = *(";" other-param)

        priovalue   = integer       ;Must be in the range [0..9]
           ; All other values are reserved for future use

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   Example:  The following is an example of a property with the highest
      priority:

        PRIORITY:1

      The following is an example of a property with a next highest
      priority:

        PRIORITY:2

      The following is an example of a property with no priority.  This
      is equivalent to not specifying the "PRIORITY" property:

        PRIORITY:0

3.8.1.10.  Resources

   Property Name:  RESOURCES

   Purpose:  This property defines the equipment or resources
      anticipated for an activity specified by a calendar component.

   Value Type:  TEXT

   Property Parameters:  IANA, non-standard, alternate text
      representation and language property parameters can be specified
      on this property.

   Conformance:  This property can be specified once in "VEVENT" or
      "VTODO" calendar component.

   Description:  The property value is an arbitrary text.  More than one
      resource can be specified as a list of resources separated by the
      COMMA character (US-ASCII decimal 44).

   Format Definition:  This property is defined by the following
      notation:

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        resources  = "RESOURCES" resrcparam ":" text *("," text) CRLF

        resrcparam = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" altrepparam) / (";" languageparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

   Example:  The following is an example of this property:

        RESOURCES:EASEL,PROJECTOR,VCR

        RESOURCES;LANGUAGE=fr:Nettoyeur haute pression

3.8.1.11.  Status

   Property Name:  STATUS

   Purpose:  This property defines the overall status or confirmation
      for the calendar component.

   Value Type:  TEXT

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified once in "VEVENT",
      "VTODO" or "VJOURNAL" calendar components.

   Description:  In a group scheduled calendar component, the property
      is used by the "Organizer" to provide a confirmation of the event
      to the "Attendees".  For example in a "VEVENT" calendar component,
      the "Organizer" can indicate that a meeting is tentative,
      confirmed or cancelled.  In a "VTODO" calendar component, the
      "Organizer" can indicate that an action item needs action, is
      completed, is in process or being worked on, or has been
      cancelled.  In a "VJOURNAL" calendar component, the "Organizer"
      can indicate that a journal entry is draft, final or has been
      cancelled or removed.

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   Format Definition:  This property is defined by the following
      notation:

        status          = "STATUS" statparam ":" statvalue CRLF

        statparam       = *(";" other-param)

        statvalue       = (statvalue-event
                        /  statvalue-todo
                        /  statvalue-jour)

        statvalue-event = "TENTATIVE"    ;Indicates event is tentative.
                        / "CONFIRMED"    ;Indicates event is definite.
                        / "CANCELLED"    ;Indicates event was cancelled.
        ;Status values for a "VEVENT"

        statvalue-todo  = "NEEDS-ACTION" ;Indicates to-do needs action.
                        / "COMPLETED"    ;Indicates to-do completed.
                        / "IN-PROCESS"   ;Indicates to-do in process of.
                        / "CANCELLED"    ;Indicates to-do was cancelled.
        ;Status values for "VTODO".

        statvalue-jour  = "DRAFT"        ;Indicates journal is draft.
                        / "FINAL"        ;Indicates journal is final.
                        / "CANCELLED"    ;Indicates journal is removed.
       ;Status values for "VJOURNAL".

   Example:  The following is an example of this property for a "VEVENT"
      calendar component:

        STATUS:TENTATIVE

      The following is an example of this property for a "VTODO"
      calendar component:

        STATUS:NEEDS-ACTION

      The following is an example of this property for a "VJOURNAL"
      calendar component:

        STATUS:DRAFT

3.8.1.12.  Summary

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   Property Name:  SUMMARY

   Purpose:  This property defines a short summary or subject for the
      calendar component.

   Value Type:  TEXT

   Property Parameters:  IANA, non-standard, alternate text
      representation and language property parameters can be specified
      on this property.

   Conformance:  The property can be specified in "VEVENT", "VTODO",
      "VJOURNAL" or "VALARM" calendar components.

   Description:  This property is used in the "VEVENT", "VTODO" and
      "VJOURNAL" calendar components to capture a short, one line
      summary about the activity or journal entry.

      This property is used in the "VALARM" calendar component to
      capture the subject of an EMAIL category of alarm.

   Format Definition:  This property is defined by the following
      notation:

        summary    = "SUMMARY" summparam ":" text CRLF

        summparam  = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" altrepparam) / (";" languageparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

   Example:  The following is an example of this property:

        SUMMARY:Department Party

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3.8.2.  Date and Time Component Properties

   The following properties specify date and time related information in
   calendar components.

3.8.2.1.  Date/Time Completed

   Property Name:  COMPLETED

   Purpose:  This property defines the date and time that a to-do was
      actually completed.

   Value Type:  DATE-TIME

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  The property can be specified in a "VTODO" calendar
      component.  The value MUST be specified as a date with UTC time.

   Description:  This property defines the date and time that a to-do
      was actually completed.

   Format Definition:  This property is defined by the following
      notation:

        completed  = "COMPLETED" compparam ":" date-time CRLF

        compparam  = *(";" other-param)

   Example:  The following is an example of this property:

     COMPLETED:19960401T150000Z

3.8.2.2.  Date/Time End

   Property Name:  DTEND

   Purpose:  This property specifies the date and time that a calendar
      component ends.

   Value Type:  The default value type is DATE-TIME.  The value type can
      be set to a DATE value type.

   Property Parameters:  IANA, non-standard, value data type, and time
      zone identifier property parameters can be specified on this
      property.

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   Conformance:  This property can be specified in "VEVENT" or
      "VFREEBUSY" calendar components.

   Description:  Within the "VEVENT" calendar component, this property
      defines the date and time by which the event ends.  The value type
      of this property MUST be the same as the "DTSTART" property, and
      its value MUST be later in time than the value of the "DTSTART"
      property.  Furthermore, this property MUST be specified as a date
      with local time if and only if the "DTSTART" property is also
      specified as a date with local time.

      Within the "VFREEBUSY" calendar component, this property defines
      the end date and time for the free or busy time information.  The
      time MUST be specified in the UTC time format.  The value MUST be
      later in time than the value of the "DTSTART" property.

   Format Definition:  This property is defined by the following
      notation:

        dtend      = "DTEND" dtendparam ":" dtendval CRLF

        dtendparam = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                   (";" tzidparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

        dtendval   = date-time / date
        ;Value MUST match value type

   Example:  The following is an example of this property:

        DTEND:19960401T150000Z

        DTEND;VALUE=DATE:19980704

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3.8.2.3.  Date/Time Due

   Property Name:  DUE

   Purpose:  This property defines the date and time that a to-do is
      expected to be completed.

   Value Type:  The default value type is DATE-TIME.  The value type can
      be set to a DATE value type.

   Property Parameters:  IANA, non-standard, value data type, and time
      zone identifier property parameters can be specified on this
      property.

   Conformance:  The property can be specified once in a "VTODO"
      calendar component.

   Description:  This property defines the date and time before which a
      to-do is expected to be completed.  For cases where this property
      is specified in a "VTODO" calendar component that also specifies a
      "DTSTART" property, the value type of this property MUST be the
      same as the "DTSTART" property, and the value of this property
      MUST be later in time than the value of the "DTSTART" property.
      Furthermore, this property MUST be specified as a date with local
      time if and only if the "DTSTART" property is also specified as a
      date with local time.

   Format Definition:  This property is defined by the following
      notation:

        due        = "DUE" dueparam ":" dueval CRLF

        dueparam   = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                   (";" tzidparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

        dueval     = date-time / date

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        ;Value MUST match value type

   Example:  The following is an example of this property:

        DUE:19980430T000000Z

3.8.2.4.  Date/Time Start

   Property Name:  DTSTART

   Purpose:  This property specifies when the calendar component begins.

   Value Type:  The default value type is DATE-TIME.  The time value
      MUST be one of the forms defined for the DATE-TIME value type.
      The value type can be set to a DATE value type.

   Property Parameters:  IANA, non-standard, value data type, and time
      zone identifier property parameters can be specified on this
      property.

   Conformance:  This property can be specified once in the "VEVENT",
      "VTODO", or "VFREEBUSY" calendar components as well as in the
      "STANDARD" and "DAYLIGHT" sub-components.  This property is
      REQUIRED in all types of recurring calendar components that
      specify the "RRULE" property.  This property is also REQUIRED in
      "VEVENT" calendar components contained in iCalendar objects that
      don't specify the "METHOD" property.

   Description:  Within the "VEVENT" calendar component, this property
      defines the start date and time for the event.

      Within the "VFREEBUSY" calendar component, this property defines
      the start date and time for the free or busy time information.
      The time MUST be specified in UTC time.

      Within the "STANDARD" and "DAYLIGHT" sub-components, this property
      defines the effective start date and time for a time zone
      specification.  This property is REQUIRED within each "STANDARD"
      and "DAYLIGHT" sub-components included in "VTIMEZONE" calendar
      components and MUST be specified as a date with local time without
      the "TZID" property parameter.

   Format Definition:  This property is defined by the following
      notation:

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        dtstart    = "DTSTART" dtstparam ":" dtstval CRLF

        dtstparam  = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                   (";" tzidparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

        dtstval    = date-time / date
        ;Value MUST match value type

   Example:  The following is an example of this property:

        DTSTART:19980118T073000Z

3.8.2.5.  Duration

   Property Name:  DURATION

   Purpose:  This property specifies a positive duration of time.

   Value Type:  DURATION

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified in "VEVENT", "VTODO", or
      "VALARM" calendar components.

   Description:  In a "VEVENT" calendar component the property may be
      used to specify a duration of the event, instead of an explicit
      end date/time.  In a "VTODO" calendar component the property may
      be used to specify a duration for the to-do, instead of an
      explicit due date/time.  In a "VALARM" calendar component the
      property may be used to specify the delay period prior to
      repeating an alarm.  When the "DURATION" property relates to a
      "DTSTART" property that is specified as a DATE value, then the
      "DURATION" property MUST be specified as a "dur-day" or "dur-week"
      value.

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   Format Definition:  This property is defined by the following
      notation:

        duration   = "DURATION" durparam ":" dur-value CRLF
                     ;consisting of a positive duration of time.

                     durparam   = *(";" other-param)

   Example:  The following is an example of this property that specifies
      an interval of time of 1 hour and zero minutes and zero seconds:

        DURATION:PT1H0M0S

      The following is an example of this property that specifies an
      interval of time of 15 minutes.

        DURATION:PT15M

3.8.2.6.  Free/Busy Time

   Property Name:  FREEBUSY

   Purpose:  This property defines one or more free or busy time
      intervals.

   Value Type:  PERIOD

   Property Parameters:  IANA, non-standard, and free/busy time type
      property parameters can be specified on this property.

   Conformance:  The property can be specified in a "VFREEBUSY" calendar
      component.

   Description:  These time periods can be specified as either a start
      and end date-time or a start date-time and duration.  The date and
      time MUST be a UTC time format.

      "FREEBUSY" properties within the "VFREEBUSY" calendar component
      SHOULD be sorted in ascending order, based on start time and then
      end time, with the earliest periods first.

      The "FREEBUSY" property can specify more than one value, separated
      by the COMMA character (US-ASCII decimal 44).  In such cases, the
      "FREEBUSY" property values MUST all be of the same "FBTYPE"
      property parameter type (e.g., all values of a particular "FBTYPE"
      listed together in a single property).

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   Format Definition:  This property is defined by the following
      notation:

        freebusy   = "FREEBUSY" fbparam ":" fbvalue CRLF

        fbparam    = *(
                   ;
                   ; the following is OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" fbtypeparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

        fbvalue    = period *("," period)
        ;Time value MUST be in the UTC time format.

   Example:  The following are some examples of this property:

        FREEBUSY;FBTYPE=BUSY-UNAVAILABLE:19970308T160000Z/PT8H30M

        FREEBUSY;FBTYPE=FREE:19970308T160000Z/PT3H,19970308T200000Z/PT1H

        FREEBUSY;FBTYPE=FREE:19970308T160000Z/PT3H,19970308T200000Z/PT1H
         ,19970308T230000Z/19970309T000000Z

3.8.2.7.  Time Transparency

   Property Name:  TRANSP

   Purpose:  This property defines whether an event is transparent or
      not to busy time searches.

   Value Type:  TEXT

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified once in a "VEVENT"
      calendar component.

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   Description:  Time Transparency is the characteristic of an event
      that determines whether it appears to consume time on a calendar.
      Events that consume actual time for the individual or resource
      associated with the calendar SHOULD be recorded as OPAQUE,
      allowing them to be detected by free-busy time searches.  Other
      events, which do not take up the individual's (or resource's) time
      SHOULD be recorded as TRANSPARENT, making them invisible to free-
      busy time searches.

   Format Definition:  This property is defined by the following
      notation:

        transp     = "TRANSP" transparam ":" transvalue CRLF

        transparam = *(";" other-param)

        transvalue = "OPAQUE"
                    ;Blocks or opaque on busy time searches.
                    / "TRANSPARENT"
                    ;Transparent on busy time searches.
        ;Default value is OPAQUE

   Example:  The following is an example of this property for an event
      that is transparent or does not block on free/busy time searches:

        TRANSP:TRANSPARENT

      The following is an example of this property for an event that is
      opaque or blocks on free/busy time searches:

        TRANSP:OPAQUE

3.8.3.  Time Zone Component Properties

   The following properties specify time zone information in calendar
   components.

3.8.3.1.  Time Zone Identifier

   Property Name:  TZID

   Purpose:  This property specifies the text value that uniquely
      identifies the "VTIMEZONE" calendar component in the scope of an
      iCalendar object.

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   Value Type:  TEXT

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property MUST be specified in a "VTIMEZONE"
      calendar component.

   Description:  This is the label by which a time zone calendar
      component is referenced by any iCalendar properties whose value
      type is either DATE-TIME or TIME and not intended to specify a UTC
      or a "floating" time.  The presence of the SOLIDUS character (US-
      ASCII decimal 47) as a prefix, indicates that this "TZID"
      represents an unique ID in a globally defined time zone registry
      (when such registry is defined).

         Note: This document does not define a naming convention for
         time zone identifiers.  Implementers may want to use the naming
         conventions defined in existing time zone specifications such
         as the public-domain TZ database [TZDB].  The specification of
         globally unique time zone identifiers is not addressed by this
         document and is left for future study.

   Format Definition:  This property is defined by the following
      notation:

        tzid       = "TZID" tzidpropparam ":" [tzidprefix] text CRLF

        tzidpropparam      = *(";" other-param)

        ;tzidprefix        = "/"
        ; Defined previously. Just listed here for reader convenience.

   Example:  The following are examples of non-globally unique time zone
      identifiers:

        TZID:America/New_York

        TZID:America/Los_Angeles

      The following is an example of a fictitious globally unique time
      zone identifier:

        TZID:/example.org/America/New_York

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3.8.3.2.  Time Zone Name

   Property Name:  TZNAME

   Purpose:  This property specifies the customary designation for a
      time zone description.

   Value Type:  TEXT

   Property Parameters:  IANA, non-standard, and language property
      parameters can be specified on this property.

   Conformance:  This property can be specified in "STANDARD" and
      "DAYLIGHT" sub-components.

   Description:  This property specifies a customary name that can be
      used when displaying dates that occur during the observance
      defined by the time zone sub-component.

   Format Definition:  This property is defined by the following
      notation:

        tzname     = "TZNAME" tznparam ":" text CRLF

        tznparam   = *(
                   ;
                   ; the following is OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" languageparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

   Example:  The following are examples of this property:

        TZNAME:EST

        TZNAME;LANGUAGE=fr-CA:HNE

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3.8.3.3.  Time Zone Offset From

   Property Name:  TZOFFSETFROM

   Purpose:  This property specifies the offset which is in use prior to
      this time zone observance.

   Value Type:  UTC-OFFSET

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property MUST be specified in "STANDARD" and
      "DAYLIGHT" sub-components.

   Description:  This property specifies the offset which is in use
      prior to this time observance.  It is used to calculate the
      absolute time at which the transition to a given observance takes
      place.  This property MUST only be specified in a "VTIMEZONE"
      calendar component.  A "VTIMEZONE" calendar component MUST include
      this property.  The property value is a signed numeric indicating
      the number of hours and possibly minutes from UTC.  Positive
      numbers represent time zones east of the prime meridian, or ahead
      of UTC.  Negative numbers represent time zones west of the prime
      meridian, or behind UTC.

   Format Definition:  This property is defined by the following
      notation:

        tzoffsetfrom       = "TZOFFSETFROM" frmparam ":" utc-offset
                             CRLF

        frmparam   = *(";" other-param)

   Example:  The following are examples of this property:

        TZOFFSETFROM:-0500

        TZOFFSETFROM:+1345

3.8.3.4.  Time Zone Offset To

   Property Name:  TZOFFSETTO

   Purpose:  This property specifies the offset which is in use in this
      time zone observance.

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   Value Type:  UTC-OFFSET

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property MUST be specified in "STANDARD" and
      "DAYLIGHT" sub-components.

   Description:  This property specifies the offset which is in use in
      this time zone observance.  It is used to calculate the absolute
      time for the new observance.  The property value is a signed
      numeric indicating the number of hours and possibly minutes from
      UTC.  Positive numbers represent time zones east of the prime
      meridian, or ahead of UTC.  Negative numbers represent time zones
      west of the prime meridian, or behind UTC.

   Format Definition:  This property is defined by the following
      notation:

        tzoffsetto = "TZOFFSETTO" toparam ":" utc-offset CRLF

        toparam    = *(";" other-param)

   Example:  The following are examples of this property:

        TZOFFSETTO:-0400

        TZOFFSETTO:+1245

3.8.3.5.  Time Zone URL

   Property Name:  TZURL

   Purpose:  This property provides a means for a "VTIMEZONE" component
      to point to a network location that can be used to retrieve an up-
      to-date version of itself.

   Value Type:  URI

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified in a "VTIMEZONE"
      calendar component.

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   Description:  This property provides a means for a "VTIMEZONE"
      component to point to a network location that can be used to
      retrieve an up-to-date version of itself.  This provides a hook to
      handle changes government bodies impose upon time zone
      definitions.  Retrieval of this resource results in an iCalendar
      object containing a single "VTIMEZONE" component and a "METHOD"
      property set to PUBLISH.

   Format Definition:  This property is defined by the following
      notation:

        tzurl      = "TZURL" tzurlparam ":" uri CRLF

        tzurlparam = *(";" other-param)

   Example:  The following is an example of this property:

     TZURL:http://timezones.example.org/tz/America-Los_Angeles.ics

3.8.4.  Relationship Component Properties

   The following properties specify relationship information in calendar
   components.

3.8.4.1.  Attendee

   Property Name:  ATTENDEE

   Purpose:  This property defines an "Attendee" within a calendar
      component.

   Value Type:  CAL-ADDRESS

   Property Parameters:  IANA, non-standard, language, calendar user
      type, group or list membership, participation role, participation
      status, RSVP expectation, delegatee, delegator, sent by, common
      name or directory entry reference property parameters can be
      specified on this property.

   Conformance:  This property MUST be specified in an iCalendar object
      that specifies a group scheduled calendar entity.  This property
      MUST NOT be specified in an iCalendar object when publishing the
      calendar information (e.g., NOT in an iCalendar object that
      specifies the publication of a calendar user's busy time, event,
      to-do or journal).  This property is not specified in an iCalendar
      object that specifies only a time zone definition or that defines
      calendar components that are not group scheduled components, but
      are components only on a single user's calendar.

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   Description:  This property MUST only be specified within calendar
      components to specify participants, non-participants and the chair
      of a group scheduled calendar entity.  The property is specified
      within an "EMAIL" category of the "VALARM" calendar component to
      specify an email address that is to receive the email type of
      iCalendar alarm.

      The property parameter "CN" is for the common or displayable name
      associated with the calendar address; "ROLE", for the intended
      role that the attendee will have in the calendar component;
      "PARTSTAT", for the status of the attendee's participation;
      "RSVP", for indicating whether the favor of a reply is requested;
      "CUTYPE", to indicate the type of calendar user; "MEMBER", to
      indicate the groups that the attendee belongs to; "DELEGATED-TO",
      to indicate the calendar users that the original request was
      delegated to; and "DELEGATED-FROM", to indicate whom the request
      was delegated from; "SENT-BY", to indicate whom is acting on
      behalf of the "ATTENDEE"; and "DIR", to indicate the URI that
      points to the directory information corresponding to the attendee.
      These property parameters can be specified on an "ATTENDEE"
      property in either a "VEVENT", "VTODO" or "VJOURNAL" calendar
      component.  They MUST NOT be specified in an "ATTENDEE" property
      in a "VFREEBUSY" or "VALARM" calendar component.  If the
      "LANGUAGE" property parameter is specified, the identified
      language applies to the "CN" parameter.

      A recipient delegated a request MUST inherit the "RSVP" and "ROLE"
      values from the attendee that delegated the request to them.

      Multiple attendees can be specified by including multiple
      "ATTENDEE" properties within the calendar component.

   Format Definition:  This property is defined by the following
      notation:

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        attendee   = "ATTENDEE" attparam ":" cal-address CRLF

        attparam   = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" cutypeparam) / (";" memberparam) /
                   (";" roleparam) / (";" partstatparam) /
                   (";" rsvpparam) / (";" deltoparam) /
                   (";" delfromparam) / (";" sentbyparam) /
                   (";" cnparam) / (";" dirparam) /
                   (";" languageparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

   Example:  The following are examples of this property's use for a
      to-do:

        ATTENDEE;MEMBER="mailto:DEV-GROUP@example.com":
         mailto:joecool@example.com
        ATTENDEE;DELEGATED-FROM="mailto:immud@example.com":
         mailto:ildoit@example.com

      The following is an example of this property used for specifying
      multiple attendees to an event:

        ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=TENTATIVE;CN=Henry
         Cabot:mailto:hcabot@example.com
        ATTENDEE;ROLE=REQ-PARTICIPANT;DELEGATED-FROM="mailto:bob@
         example.com";PARTSTAT=ACCEPTED;CN=Jane Doe:mailto:jdoe@
         example.com

      The following is an example of this property with a URI to the
      directory information associated with the attendee:

        ATTENDEE;CN=John Smith;DIR="ldap://example.com:6666/o=ABC%
         20Industries,c=US???(cn=Jim%20Dolittle)":mailto:jimdo@
         example.com

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      The following is an example of this property with "delegatee" and
      "delegator" information for an event:

        ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=TENTATIVE;DELEGATED-FROM=
         "mailto:iamboss@example.com";CN=Henry Cabot:mailto:hcabot@
         example.com
        ATTENDEE;ROLE=NON-PARTICIPANT;PARTSTAT=DELEGATED;DELEGATED-TO=
         "mailto:hcabot@example.com";CN=The Big Cheese:mailto:iamboss
         @example.com
        ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED;CN=Jane Doe
         :mailto:jdoe@example.com

   Example:  The following is an example of this property's use when
      another calendar user is acting on behalf of the "Attendee":

        ATTENDEE;SENT-BY=mailto:jan_doe@example.com;CN=John Smith:
         mailto:jsmith@example.com

3.8.4.2.  Contact

   Property Name:  CONTACT

   Purpose:  This property is used to represent contact information or
      alternately a reference to contact information associated with the
      calendar component.

   Value Type:  TEXT

   Property Parameters:  IANA, non-standard, alternate text
      representation and language property parameters can be specified
      on this property.

   Conformance:  This property can be specified in a "VEVENT", "VTODO",
      "VJOURNAL" or "VFREEBUSY" calendar component.

   Description:  The property value consists of textual contact
      information.  An alternative representation for the property value
      can also be specified that refers to a URI pointing to an
      alternate form, such as a vCard [RFC2426], for the contact
      information.

   Format Definition:  This property is defined by the following
      notation:

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        contact    = "CONTACT" contparam ":" text CRLF

        contparam  = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" altrepparam) / (";" languageparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

   Example:  The following is an example of this property referencing
      textual contact information:

        CONTACT:Jim Dolittle\, ABC Industries\, +1-919-555-1234

      The following is an example of this property with an alternate
      representation of a LDAP URI to a directory entry containing the
      contact information:

        CONTACT;ALTREP="ldap://example.com:6666/o=ABC%20Industries\,
         c=US???(cn=Jim%20Dolittle)":Jim Dolittle\, ABC Industries\,
         +1-919-555-1234

      The following is an example of this property with an alternate
      representation of a MIME body part containing the contact
      information, such as a vCard [RFC2426] embedded in a text/
      directory media type [RFC2425]:

        CONTACT;ALTREP="CID:part3.msg970930T083000SILVER@example.com":
         Jim Dolittle\, ABC Industries\, +1-919-555-1234

      The following is an example of this property referencing a network
      resource, such as a vCard [RFC2426] object containing the contact
      information:

        CONTACT;ALTREP="http://example.com/pdi/jdoe.vcf":Jim
          Dolittle\, ABC Industries\, +1-919-555-1234

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3.8.4.3.  Organizer

   Property Name:  ORGANIZER

   Purpose:  This property defines the organizer for a calendar
      component.

   Value Type:  CAL-ADDRESS

   Property Parameters:  IANA, non-standard, language, common name,
      directory entry reference, sent by property parameters can be
      specified on this property.

   Conformance:  This property MUST be specified in an iCalendar object
      that specifies a group scheduled calendar entity.  This property
      MUST be specified in an iCalendar object that specifies the
      publication of a calendar user's busy time.  This property MUST
      NOT be specified in an iCalendar object that specifies only a time
      zone definition or that defines calendar components that are not
      group scheduled components, but are components only on a single
      user's calendar.

   Description:  This property is specified within the "VEVENT",
      "VTODO", "VJOURNAL" calendar components to specify the organizer
      of a group scheduled calendar entity.  The property is specified
      within the "VFREEBUSY" calendar component to specify the calendar
      user requesting the free or busy time.  When publishing a
      "VFREEBUSY" calendar component, the property is used to specify
      the calendar that the published busy time came from.

      The property has the property parameters "CN", for specifying the
      common or display name associated with the "Organizer", "DIR", for
      specifying a pointer to the directory information associated with
      the "Organizer", "SENT-BY", for specifying another calendar user
      that is acting on behalf of the "Organizer".  The non-standard
      parameters may also be specified on this property.  If the
      "LANGUAGE" property parameter is specified, the identified
      language applies to the "CN" parameter value.

   Format Definition:  This property is defined by the following
      notation:

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        organizer  = "ORGANIZER" orgparam ":"
                     cal-address CRLF

        orgparam   = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" cnparam) / (";" dirparam) / (";" sentbyparam) /
                   (";" languageparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

   Example:  The following is an example of this property:

        ORGANIZER;CN=John Smith:mailto:jsmith@example.com

      The following is an example of this property with a pointer to the
      directory information associated with the organizer:

        ORGANIZER;CN=JohnSmith;DIR="ldap://example.com:6666/o=DC%20Ass
         ociates,c=US???(cn=John%20Smith)":mailto:jsmith@example.com

      The following is an example of this property used by another
      calendar user who is acting on behalf of the organizer, with
      responses intended to be sent back to the organizer, not the other
      calendar user:

        ORGANIZER;SENT-BY="mailto:jane_doe@example.com":
         mailto:jsmith@example.com

3.8.4.4.  Recurrence ID

   Property Name:  RECURRENCE-ID

   Purpose:  This property is used in conjunction with the "UID" and
      "SEQUENCE" property to identify a specific instance of a recurring
      "VEVENT", "VTODO" or "VJOURNAL" calendar component.  The property
      value is the original value of the "DTSTART" property of the
      recurrence instance.

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   Value Type:  The default value type for this property is DATE-TIME.
      The default value type is DATE-TIME.  The value type can be set to
      a DATE value type.  This property MUST have the same value type as
      the "DTSTART" property contained within the recurring component.
      Furthermore, this property MUST be specified as a date with local
      time if and only if the "DTSTART" property contained within the
      recurring component is specified as a date with local time.

   Property Parameters:  IANA, non-standard, value data type, time zone
      identifier and recurrence identifier range parameters can be
      specified on this property.

   Conformance:  This property can be specified in an iCalendar object
      containing a recurring calendar component.

   Description:  The full range of calendar components specified by a
      recurrence set is referenced by referring to just the "UID"
      property value corresponding to the calendar component.  The
      "RECURRENCE-ID" property allows the reference to an individual
      instance within the recurrence set.

      If the value of the "DTSTART" property is a DATE type value, then
      the value MUST be the calendar date for the recurrence instance.

      The DATE-TIME value is set to the time when the original
      recurrence instance would occur; meaning that if the intent is to
      change a Friday meeting to Thursday, the DATE-TIME is still set to
      the original Friday meeting.

      The "RECURRENCE-ID" property is used in conjunction with the "UID"
      and "SEQUENCE" property to identify a particular instance of a
      recurring event, to-do or journal.  For a given pair of "UID" and
      "SEQUENCE" property values, the "RECURRENCE-ID" value for a
      recurrence instance is fixed.

      The "RANGE" parameter is used to specify the effective range of
      recurrence instances from the instance specified by the
      "RECURRENCE-ID" property value.  The value for the range parameter
      can only be "THISANDFUTURE" to indicate a range defined by the
      given recurrence instance and all subsequent instances.
      Subsequent instances are determined by their "RECURRENCE-ID" value
      and not their current scheduled start time.  Subsequent instances
      defined in separate components are not impacted by the given
      recurrence instance.  When the given recurrence instance is
      rescheduled, all subsequent instances are also rescheduled by the
      same time difference.  For instance, if the given recurrence
      instance is rescheduled to start 2 hours later, then all
      subsequent instances are also rescheduled 2 hours later.

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      Similarly, if the duration of the given recurrence instance is
      modified, then all subsequence instances are also modified to have
      this same duration.

         Note: The "RANGE" parameter may not be appropriate to
         reschedule specific subsequent instances of complex recurring
         calendar component.  Assuming an unbounded recurring calendar
         component scheduled to occur on Mondays and Wednesdays, the
         "RANGE" parameter could not be used to reschedule only the
         future Monday instances to occur on Tuesday instead.  In such
         cases, the calendar application could simply truncate the
         unbounded recurring calendar component (i.e., with the "COUNT"
         or "UNTIL" rule parts), and create two new unbounded recurring
         calendar components for the future instances.

   Format Definition:  This property is defined by the following
      notation:

          recurid    = "RECURRENCE-ID" ridparam ":" ridval CRLF

        ridparam   = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                   (";" tzidparam) / (";" rangeparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

        ridval     = date-time / date
        ;Value MUST match value type

   Example:  The following are examples of this property:

        RECURRENCE-ID;VALUE=DATE:19960401

        RECURRENCE-ID;RANGE=THISANDFUTURE:19960120T120000Z

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3.8.4.5.  Related To

   Property Name:  RELATED-TO

   Purpose:  This property is used to represent a relationship or
      reference between one calendar component and another.

   Value Type:  TEXT

   Property Parameters:  IANA, non-standard, and relationship type
      property parameters can be specified on this property.

   Conformance:  This property can be specified in the "VEVENT", "VTODO"
      and "VJOURNAL" calendar components.

   Description:  The property value consists of the persistent, globally
      unique identifier of another calendar component.  This value would
      be represented in a calendar component by the "UID" property.

      By default, the property value points to another calendar
      component that has a PARENT relationship to the referencing
      object.  The "RELTYPE" property parameter is used to either
      explicitly state the default PARENT relationship type to the
      referenced calendar component or to override the default PARENT
      relationship type and specify either a CHILD or SIBLING
      relationship.  The PARENT relationship indicates that the calendar
      component is a subordinate of the referenced calendar component.
      The CHILD relationship indicates that the calendar component is a
      superior of the referenced calendar component.  The SIBLING
      relationship indicates that the calendar component is a peer of
      the referenced calendar component.

      Changes to a calendar component referenced by this property can
      have an implicit impact on the related calendar component.  For
      example, if a group event changes its start or end date or time,
      then the related, dependent events will need to have their start
      and end dates changed in a corresponding way.  Similarly, if a
      PARENT calendar component is cancelled or deleted, then there is
      an implied impact to the related CHILD calendar components.  This
      property is intended only to provide information on the
      relationship of calendar components.  It is up to the target
      calendar system to maintain any property implications of this
      relationship.

   Format Definition:  This property is defined by the following
      notation:

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        related    = "RELATED-TO" relparam ":" text CRLF

        relparam   = *(
                   ;
                   ; the following is OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" reltypeparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

      The following is an example of this property:

        RELATED-TO:jsmith.part7.19960817T083000.xyzMail@example.com

        RELATED-TO:19960401-080045-4000F192713-0052@example.com

3.8.4.6.  Uniform Resource Locator

   Property Name:  URL

   Purpose:  This property defines a Uniform Resource Locator (URL)
      associated with the iCalendar object.

   Value Type:  URI

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified once in the "VEVENT",
      "VTODO", "VJOURNAL" or "VFREEBUSY" calendar components.

   Description:  This property may be used in a calendar component to
      convey a location where a more dynamic rendition of the calendar
      information associated with the calendar component can be found.
      This memo does not attempt to standardize the form of the URI, nor
      the format of the resource pointed to by the property value.  If
      the URL property and Content-Location MIME header are both
      specified, they MUST point to the same resource.

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   Format Definition:  This property is defined by the following
      notation:

        url        = "URL" urlparam ":" uri CRLF

        urlparam   = *(";" other-param)

   Example:  The following is an example of this property:

        URL:http://example.com/pub/calendars/jsmith/mytime.ics

3.8.4.7.  Unique Identifier

   Property Name:  UID

   Purpose:  This property defines the persistent, globally unique
      identifier for the calendar component.

   Value Type:  TEXT

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  The property MUST be specified in the "VEVENT",
      "VTODO", "VJOURNAL" or "VFREEBUSY" calendar components.

   Description:  The "UID" itself MUST be a globally unique identifier.
      The generator of the identifier MUST guarantee that the identifier
      is unique.  There are several algorithms that can be used to
      accomplish this.  A good method to assure uniqueness is to put the
      domain name or a domain literal IP address of the host on which
      the identifier was created on the right hand side of an "@", and
      on the left hand side, put a combination of the current calendar
      date and time of day (i.e., formatted in as a DATE-TIME value)
      along with some other currently unique (perhaps sequential)
      identifier available on the system (for example, a process id
      number).  Using a date/time value on the left hand side and a
      domain name or domain literal on the right hand side makes it
      possible to guarantee uniqueness since no two hosts should be
      using the same domain name or IP address at the same time.  Though
      other algorithms will work, it is RECOMMENDED that the right hand
      side contain some domain identifier (either of the host itself or
      otherwise) such that the generator of the message identifier can
      guarantee the uniqueness of the left hand side within the scope of
      that domain.

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      This is the method for correlating scheduling messages with the
      referenced "VEVENT", "VTODO", or "VJOURNAL" calendar component.

      The full range of calendar components specified by a recurrence
      set is referenced by referring to just the "UID" property value
      corresponding to the calendar component.  The "RECURRENCE-ID"
      property allows the reference to an individual instance within the
      recurrence set.

      This property is an important method for group scheduling
      applications to match requests with later replies, modifications
      or deletion requests.  Calendaring and scheduling applications
      MUST generate this property in "VEVENT", "VTODO" and "VJOURNAL"
      calendar components to assure interoperability with other group
      scheduling applications.  This identifier is created by the
      calendar system that generates an iCalendar object.

      Implementations MUST be able to receive and persist values of at
      least 255 octets for this property but MUST NOT truncate values in
      the middle of a UTF-8 multi-octet sequence.

   Format Definition:  This property is defined by the following
      notation:

        uid        = "UID" uidparam ":" text CRLF

        uidparam   = *(";" other-param)

   Example:  The following is an example of this property:

        UID:19960401T080045Z-4000F192713-0052@example.com

3.8.5.  Recurrence Component Properties

   The following properties specify recurrence information in calendar
   components.

3.8.5.1.  Exception Date/Times

   Property Name:  EXDATE

   Purpose:  This property defines the list of date/time exceptions for
      recurring events, to-dos, journal entries or time zone
      definitions.

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   Value Type:  The default value type for this property is DATE-TIME.
      The value type can be set to DATE.

   Property Parameters:  IANA, non-standard, value data type and time
      zone identifier property parameters can be specified on this
      property.

   Conformance:  This property can be specified in recurring "VEVENT",
      "VTODO", and "VJOURNAL" calendar components as well as in the
      "STANDARD" and "DAYLIGHT" sub-components of the "VTIMEZONE"
      calendar component.

   Description:  The exception dates, if specified, are used in
      computing the recurrence set.  The recurrence set is the complete
      set of recurrence instances for a calendar component.  The
      recurrence set is generated by considering the initial "DTSTART"
      property along with the "RRULE", "RDATE", and "EXDATE" properties
      contained within the recurring component.  The "DTSTART" property
      defines the first instance in the recurrence set.  The "DTSTART"
      property value SHOULD match the pattern of the recurrence rule, if
      specified.  The recurrence set generated with a "DTSTART" property
      value that doesn't match the pattern of the rule is undefined.
      The final recurrence set is generated by gathering all of the
      start date-times generated by any of the specified "RRULE" and
      "RDATE" properties, and then excluding any start date and times
      specified by "EXDATE" properties.  This implies that start date
      and times specified by "EXDATE" properties take precedence over
      those specified by inclusion properties (i.e., "RDATE" and
      "RRULE").  When duplicate instances are generated by the "RRULE"
      and "RDATE" properties, only one recurrence is considered.
      Duplicate instances are ignored.

      The "EXDATE" property can be used to exclude the value specified
      in "DTSTART".  However, in such cases the original "DTSTART" date
      MUST still be maintained by the calendaring and scheduling system
      because the original "DTSTART" value has inherent usage
      dependencies by other properties such as the "RECURRENCE-ID".

   Format Definition:  This property is defined by the following
      notation:

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        exdate     = "EXDATE" exdtparam ":" exdtval *("," exdtval) CRLF

        exdtparam  = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                   ;
                   (";" tzidparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

        exdtval    = date-time / date
        ;Value MUST match value type

   Example:  The following is an example of this property:

        EXDATE:19960402T010000Z,19960403T010000Z,19960404T010000Z

3.8.5.2.  Recurrence Date/Times

   Property Name:  RDATE

   Purpose:  This property defines the list of date/times for recurring
      events, to-dos, journal entries or time zone definitions.

   Value Type:  The default value type for this property is DATE-TIME.
      The value type can be set to DATE or PERIOD.

   Property Parameters:  IANA, non-standard, value data type and time
      zone identifier property parameters can be specified on this
      property.

   Conformance:  This property can be specified in recurring "VEVENT",
      "VTODO", and "VJOURNAL" calendar components as well as in the
      "STANDARD" and "DAYLIGHT" sub-components of the "VTIMEZONE"
      calendar component.

   Description:  This property can appear along with the "RRULE"
      property to define an aggregate set of repeating occurrences.
      When they both appear in a recurring component, the recurrence
      instances are defined by the union of occurrences defined by both

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      the "RDATE" and "RRULE".

      The recurrence dates, if specified, are used in computing the
      recurrence set.  The recurrence set is the complete set of
      recurrence instances for a calendar component.  The recurrence set
      is generated by considering the initial "DTSTART" property along
      with the "RRULE", "RDATE", and "EXDATE" properties contained
      within the recurring component.  The "DTSTART" property defines
      the first instance in the recurrence set.  The "DTSTART" property
      value SHOULD match the pattern of the recurrence rule, if
      specified.  The recurrence set generated with a "DTSTART" property
      value that doesn't match the pattern of the rule is undefined.
      The final recurrence set is generated by gathering all of the
      start date-times generated by any of the specified "RRULE" and
      "RDATE" properties, and then excluding any start date and times
      specified by "EXDATE" properties.  This implies that start date/
      times specified by "EXDATE" properties take precedence over those
      specified by inclusion properties (i.e., "RDATE" and "RRULE").
      Where duplicate instances are generated by the "RRULE" and "RDATE"
      properties, only one recurrence is considered.  Duplicate
      instances are ignored.

   Format Definition:  This property is defined by the following
      notation:

        rdate      = "RDATE" rdtparam ":" rdtval *("," rdtval) CRLF

        rdtparam   = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" "VALUE" "=" ("DATE-TIME" / "DATE" / "PERIOD")) /
                   (";" tzidparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

        rdtval     = date-time / date / period
        ;Value MUST match value type

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   Example:  The following are examples of this property:

        RDATE:19970714T123000Z
        RDATE;TZID=America/New_York:19970714T083000

        RDATE;VALUE=PERIOD:19960403T020000Z/19960403T040000Z,
         19960404T010000Z/PT3H

        RDATE;VALUE=DATE:19970101,19970120,19970217,19970421
         19970526,19970704,19970901,19971014,19971128,19971129,19971225

3.8.5.3.  Recurrence Rule

   Property Name:  RRULE

   Purpose:  This property defines a rule or repeating pattern for
      recurring events, to-dos, journal entries or time zone
      definitions.

   Value Type:  RECUR

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified in recurring "VEVENT",
      "VTODO" and "VJOURNAL" calendar components as well as in the
      "STANDARD" and "DAYLIGHT" sub-components of the "VTIMEZONE"
      calendar component, but it SHOULD NOT be specified more than once.
      The recurrence set generated with multiple "RRULE" properties is
      undefined.

   Description:  The recurrence rule, if specified, is used in computing
      the recurrence set.  The recurrence set is the complete set of
      recurrence instances for a calendar component.  The recurrence set
      is generated by considering the initial "DTSTART" property along
      with the "RRULE", "RDATE", and "EXDATE" properties contained
      within the recurring component.  The "DTSTART" property defines
      the first instance in the recurrence set.  The "DTSTART" property
      value SHOULD be synchronized with the recurrence rule, if
      specified.  The recurrence set generated with a "DTSTART" property
      value not synchronized with the recurrence rule is undefined.  The
      final recurrence set is generated by gathering all of the start
      date/times generated by any of the specified "RRULE" and "RDATE"
      properties, and then excluding any start date/times specified by
      "EXDATE" properties.  This implies that start date/times specified
      by "EXDATE" properties take precedence over those specified by
      inclusion properties (i.e., "RDATE" and "RRULE").  Where duplicate
      instances are generated by the "RRULE" and "RDATE" properties,

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      only one recurrence is considered.  Duplicate instances are
      ignored.

      The "DTSTART" property specified within the iCalendar object
      defines the first instance of the recurrence.  In most cases, a
      "DTSTART" property of DATE-TIME value type used with a recurrence
      rule, should be specified as a date with local time and time zone
      reference to make sure all the recurrence instances start at the
      same local time regardless of time zone changes.

      If the duration of the recurring component is specified with the
      "DTEND" or "DUE" property, then the same exact duration will apply
      to all the members of the generated recurrence set.  Else, if the
      duration of the recurring component is specified with the
      "DURATION" property, then the same nominal duration will apply to
      all the members of the generated recurrence set and the exact
      duration of each recurrence instance will depend on its specific
      start time.  For example, recurrence instances of a nominal
      duration of one day will have an exact duration of more or less
      than 24 hours on a day where a time zone shift occurs.  The
      duration of a specific recurrence may be modified in an exception
      component or simply by using an "RDATE" property of PERIOD value
      type.

   Format Definition:  This property is defined by the following
      notation:

        rrule      = "RRULE" rrulparam ":" recur CRLF

        rrulparam  = *(";" other-param)

   Example:  All examples assume the Eastern United States time zone.

      Daily for 10 occurrences:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=DAILY;COUNT=10

        ==> (1997 9:00 AM EDT) September 2-11

      Daily until December 24, 1997:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=DAILY;UNTIL=19971224T000000Z

        ==> (1997 9:00 AM EDT) September 2-30;October 1-25
            (1997 9:00 AM EST) October 26-31;November 1-30;December 1-23

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      Every other day - forever:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=DAILY;INTERVAL=2

        ==> (1997 9:00 AM EDT) September 2,4,6,8...24,26,28,30;
                               October 2,4,6...20,22,24
            (1997 9:00 AM EST) October 26,28,30;
                               November 1,3,5,7...25,27,29;
                               December 1,3,...

      Every 10 days, 5 occurrences:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=DAILY;INTERVAL=10;COUNT=5

        ==> (1997 9:00 AM EDT) September 2,12,22;
                               October 2,12

      Everyday in January, for 3 years:

        DTSTART;TZID=America/New_York:19980101T090000

        RRULE:FREQ=YEARLY;UNTIL=20000131T140000Z;
         BYMONTH=1;BYDAY=SU,MO,TU,WE,TH,FR,SA
        or
        RRULE:FREQ=DAILY;UNTIL=20000131T140000Z;BYMONTH=1

        ==> (1998 9:00 AM EST)January 1-31
            (1999 9:00 AM EST)January 1-31
            (2000 9:00 AM EST)January 1-31

      Weekly for 10 occurrences

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=WEEKLY;COUNT=10

        ==> (1997 9:00 AM EDT) September 2,9,16,23,30;October 7,14,21
            (1997 9:00 AM EST) October 28;November 4

      Weekly until December 24, 1997

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        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=WEEKLY;UNTIL=19971224T000000Z

        ==> (1997 9:00 AM EDT) September 2,9,16,23,30;
                               October 7,14,21
            (1997 9:00 AM EST) October 28;
                               November 4,11,18,25;
                               December 2,9,16,23

      Every other week - forever:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=WEEKLY;INTERVAL=2;WKST=SU

        ==> (1997 9:00 AM EDT) September 2,16,30;
                               October 14
            (1997 9:00 AM EST) October 28;
                               November 11,25;
                               December 9,23
            (1998 9:00 AM EST) January 6,20;
                               February 3, 17
            ...

      Weekly on Tuesday and Thursday for 5 weeks:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=WEEKLY;UNTIL=19971007T000000Z;WKST=SU;BYDAY=TU,TH

        or

        RRULE:FREQ=WEEKLY;COUNT=10;WKST=SU;BYDAY=TU,TH

        ==> (1997 9:00 AM EDT) September 2,4,9,11,16,18,23,25,30;
                               October 2

      Every other week on Monday, Wednesday and Friday until December
      24, 1997, starting on Monday, September 1, 1997:

        DTSTART;TZID=America/New_York:19970901T090000
        RRULE:FREQ=WEEKLY;INTERVAL=2;UNTIL=19971224T000000Z;WKST=SU;
         BYDAY=MO,WE,FR

        ==> (1997 9:00 AM EDT) September 1,3,5,15,17,19,29;
                               October 1,3,13,15,17
            (1997 9:00 AM EST) October 27,29,31;
                               November 10,12,14,24,26,28;
                               December 8,10,12,22

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      Every other week on Tuesday and Thursday, for 8 occurrences:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=8;WKST=SU;BYDAY=TU,TH

        ==> (1997 9:00 AM EDT) September 2,4,16,18,30;
                               October 2,14,16

      Monthly on the 1st Friday for ten occurrences:

        DTSTART;TZID=America/New_York:19970905T090000
        RRULE:FREQ=MONTHLY;COUNT=10;BYDAY=1FR

        ==> (1997 9:00 AM EDT) September 5;October 3
            (1997 9:00 AM EST) November 7;December 5
            (1998 9:00 AM EST) January 2;February 6;March 6;April 3
            (1998 9:00 AM EDT) May 1;June 5

      Monthly on the 1st Friday until December 24, 1997:

        DTSTART;TZID=America/New_York:19970905T090000
        RRULE:FREQ=MONTHLY;UNTIL=19971224T000000Z;BYDAY=1FR

        ==> (1997 9:00 AM EDT) September 5; October 3
            (1997 9:00 AM EST) November 7; December 5

      Every other month on the 1st and last Sunday of the month for 10
      occurrences:

        DTSTART;TZID=America/New_York:19970907T090000
        RRULE:FREQ=MONTHLY;INTERVAL=2;COUNT=10;BYDAY=1SU,-1SU

        ==> (1997 9:00 AM EDT) September 7,28
            (1997 9:00 AM EST) November 2,30
            (1998 9:00 AM EST) January 4,25;March 1,29
            (1998 9:00 AM EDT) May 3,31

      Monthly on the second to last Monday of the month for 6 months:

        DTSTART;TZID=America/New_York:19970922T090000
        RRULE:FREQ=MONTHLY;COUNT=6;BYDAY=-2MO

        ==> (1997 9:00 AM EDT) September 22;October 20
            (1997 9:00 AM EST) November 17;December 22
            (1998 9:00 AM EST) January 19;February 16

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      Monthly on the third to the last day of the month, forever:

        DTSTART;TZID=America/New_York:19970928T090000
        RRULE:FREQ=MONTHLY;BYMONTHDAY=-3

        ==> (1997 9:00 AM EDT) September 28
            (1997 9:00 AM EST) October 29;November 28;December 29
            (1998 9:00 AM EST) January 29;February 26
            ...

      Monthly on the 2nd and 15th of the month for 10 occurrences:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=MONTHLY;COUNT=10;BYMONTHDAY=2,15

        ==> (1997 9:00 AM EDT) September 2,15;October 2,15
            (1997 9:00 AM EST) November 2,15;December 2,15
            (1998 9:00 AM EST) January 2,15

      Monthly on the first and last day of the month for 10 occurrences:

        DTSTART;TZID=America/New_York:19970930T090000
        RRULE:FREQ=MONTHLY;COUNT=10;BYMONTHDAY=1,-1

        ==> (1997 9:00 AM EDT) September 30;October 1
            (1997 9:00 AM EST) October 31;November 1,30;December 1,31
            (1998 9:00 AM EST) January 1,31;February 1

      Every 18 months on the 10th thru 15th of the month for 10
      occurrences:

        DTSTART;TZID=America/New_York:19970910T090000
        RRULE:FREQ=MONTHLY;INTERVAL=18;COUNT=10;BYMONTHDAY=10,11,12,
         13,14,15

        ==> (1997 9:00 AM EDT) September 10,11,12,13,14,15
            (1999 9:00 AM EST) March 10,11,12,13

      Every Tuesday, every other month:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=MONTHLY;INTERVAL=2;BYDAY=TU

        ==> (1997 9:00 AM EDT) September 2,9,16,23,30
            (1997 9:00 AM EST) November 4,11,18,25
            (1998 9:00 AM EST) January 6,13,20,27;March 3,10,17,24,31
            ...

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      Yearly in June and July for 10 occurrences:

        DTSTART;TZID=America/New_York:19970610T090000
        RRULE:FREQ=YEARLY;COUNT=10;BYMONTH=6,7

        ==> (1997 9:00 AM EDT) June 10;July 10
            (1998 9:00 AM EDT) June 10;July 10
            (1999 9:00 AM EDT) June 10;July 10
            (2000 9:00 AM EDT) June 10;July 10
            (2001 9:00 AM EDT) June 10;July 10

         Note: Since none of the BYDAY, BYMONTHDAY or BYYEARDAY
         components are specified, the day is gotten from "DTSTART"

      Every other year on January, February, and March for 10
      occurrences:

        DTSTART;TZID=America/New_York:19970310T090000
        RRULE:FREQ=YEARLY;INTERVAL=2;COUNT=10;BYMONTH=1,2,3

        ==> (1997 9:00 AM EST) March 10
            (1999 9:00 AM EST) January 10;February 10;March 10
            (2001 9:00 AM EST) January 10;February 10;March 10
            (2003 9:00 AM EST) January 10;February 10;March 10

      Every 3rd year on the 1st, 100th and 200th day for 10 occurrences:

        DTSTART;TZID=America/New_York:19970101T090000
        RRULE:FREQ=YEARLY;INTERVAL=3;COUNT=10;BYYEARDAY=1,100,200

        ==> (1997 9:00 AM EST) January 1
            (1997 9:00 AM EDT) April 10;July 19
            (2000 9:00 AM EST) January 1
            (2000 9:00 AM EDT) April 9;July 18
            (2003 9:00 AM EST) January 1
            (2003 9:00 AM EDT) April 10;July 19
            (2006 9:00 AM EST) January 1

      Every 20th Monday of the year, forever:

        DTSTART;TZID=America/New_York:19970519T090000
        RRULE:FREQ=YEARLY;BYDAY=20MO

        ==> (1997 9:00 AM EDT) May 19
            (1998 9:00 AM EDT) May 18
            (1999 9:00 AM EDT) May 17
            ...

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      Monday of week number 20 (where the default start of the week is
      Monday), forever:

        DTSTART;TZID=America/New_York:19970512T090000
        RRULE:FREQ=YEARLY;BYWEEKNO=20;BYDAY=MO

        ==> (1997 9:00 AM EDT) May 12
            (1998 9:00 AM EDT) May 11
            (1999 9:00 AM EDT) May 17
            ...

      Every Thursday in March, forever:

        DTSTART;TZID=America/New_York:19970313T090000
        RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=TH

        ==> (1997 9:00 AM EST) March 13,20,27
            (1998 9:00 AM EST) March 5,12,19,26
            (1999 9:00 AM EST) March 4,11,18,25
            ...

      Every Thursday, but only during June, July, and August, forever:

        DTSTART;TZID=America/New_York:19970605T090000
        RRULE:FREQ=YEARLY;BYDAY=TH;BYMONTH=6,7,8

        ==> (1997 9:00 AM EDT) June 5,12,19,26;July 3,10,17,24,31;
                               August 7,14,21,28
            (1998 9:00 AM EDT) June 4,11,18,25;July 2,9,16,23,30;
                               August 6,13,20,27
            (1999 9:00 AM EDT) June 3,10,17,24;July 1,8,15,22,29;
                               August 5,12,19,26
            ...

      Every Friday the 13th, forever:

        DTSTART;TZID=America/New_York:19970902T090000
        EXDATE;TZID=America/New_York:19970902T090000
        RRULE:FREQ=MONTHLY;BYDAY=FR;BYMONTHDAY=13

        ==> (1998 9:00 AM EST) February 13;March 13;November 13
            (1999 9:00 AM EDT) August 13
            (2000 9:00 AM EDT) October 13
            ...

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      The first Saturday that follows the first Sunday of the month,
      forever:

        DTSTART;TZID=America/New_York:19970913T090000
        RRULE:FREQ=MONTHLY;BYDAY=SA;BYMONTHDAY=7,8,9,10,11,12,13

        ==> (1997 9:00 AM EDT) September 13;October 11
            (1997 9:00 AM EST) November 8;December 13
            (1998 9:00 AM EST) January 10;February 7;March 7
            (1998 9:00 AM EDT) April 11;May 9;June 13...
            ...

      Every four years, the first Tuesday after a Monday in November,
      forever (U.S. Presidential Election day):

        DTSTART;TZID=America/New_York:19961105T090000
        RRULE:FREQ=YEARLY;INTERVAL=4;BYMONTH=11;BYDAY=TU;
         BYMONTHDAY=2,3,4,5,6,7,8

         ==> (1996 9:00 AM EST) November 5
             (2000 9:00 AM EST) November 7
             (2004 9:00 AM EST) November 2
             ...

      The 3rd instance into the month of one of Tuesday, Wednesday or
      Thursday, for the next 3 months:

        DTSTART;TZID=America/New_York:19970904T090000
        RRULE:FREQ=MONTHLY;COUNT=3;BYDAY=TU,WE,TH;BYSETPOS=3

        ==> (1997 9:00 AM EDT) September 4;October 7
            (1997 9:00 AM EST) November 6

      The 2nd to last weekday of the month:

        DTSTART;TZID=America/New_York:19970929T090000
        RRULE:FREQ=MONTHLY;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=-2

        ==> (1997 9:00 AM EDT) September 29
            (1997 9:00 AM EST) October 30;November 27;December 30
            (1998 9:00 AM EST) January 29;February 26;March 30
            ...

      Every 3 hours from 9:00 AM to 5:00 PM on a specific day:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=HOURLY;INTERVAL=3;UNTIL=19970902T170000Z

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        ==> (September 2, 1997 EDT) 09:00,12:00,15:00

      Every 15 minutes for 6 occurrences:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=MINUTELY;INTERVAL=15;COUNT=6

        ==> (September 2, 1997 EDT) 09:00,09:15,09:30,09:45,10:00,10:15

      Every hour and a half for 4 occurrences:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=MINUTELY;INTERVAL=90;COUNT=4

        ==> (September 2, 1997 EDT) 09:00,10:30;12:00;13:30

      Every 20 minutes from 9:00 AM to 4:40 PM every day:

        DTSTART;TZID=America/New_York:19970902T090000
        RRULE:FREQ=DAILY;BYHOUR=9,10,11,12,13,14,15,16;BYMINUTE=0,20,40
        or
        RRULE:FREQ=MINUTELY;INTERVAL=20;BYHOUR=9,10,11,12,13,14,15,16

        ==> (September 2, 1997 EDT) 9:00,9:20,9:40,10:00,10:20,
                                    ... 16:00,16:20,16:40
            (September 3, 1997 EDT) 9:00,9:20,9:40,10:00,10:20,
                                    ...16:00,16:20,16:40
            ...

      An example where the days generated makes a difference because of
      WKST:

        DTSTART;TZID=America/New_York:19970805T090000
        RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=4;BYDAY=TU,SU;WKST=MO

        ==> (1997 EDT) August 5,10,19,24

      changing only WKST from MO to SU, yields different results...

        DTSTART;TZID=America/New_York:19970805T090000
        RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=4;BYDAY=TU,SU;WKST=SU

        ==> (1997 EDT) August 5,17,19,31

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      An example where an invalid date (i.e., February 30) is ignored.

        DTSTART;TZID=America/New_York:20070115T090000
        RRULE:FREQ=MONTHLY;BYMONTHDAY=15,30;COUNT=5

        ==> (2007 EST) January 15,30
            (2007 EST) February 15
            (2007 EDT) March 15,30

3.8.6.  Alarm Component Properties

   The following properties specify alarm information in calendar
   components.

3.8.6.1.  Action

   Property Name:  ACTION

   Purpose:  This property defines the action to be invoked when an
      alarm is triggered.

   Value Type:  TEXT

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property MUST be specified once in a "VALARM"
      calendar component.

   Description:  Each "VALARM" calendar component has a particular type
      of action associated with it.  This property specifies the type of
      action.  Applications MUST ignore alarms with x-name and iana-
      token value they don't recognize.

   Format Definition:  This property is defined by the following
      notation:

        action      = "ACTION" actionparam ":" actionvalue CRLF

        actionparam = *(";" other-param)

        actionvalue = "AUDIO" / "DISPLAY" / "EMAIL"
                    / iana-token / x-name

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   Example:  The following are examples of this property in a "VALARM"
      calendar component:

        ACTION:AUDIO

        ACTION:DISPLAY

3.8.6.2.  Repeat Count

   Property Name:  REPEAT

   Purpose:  This property defines the number of times the alarm should
      be repeated, after the initial trigger.

   Value Type:  INTEGER

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified in a "VALARM" calendar
      component.

   Description:  This property defines the number of time an alarm
      should be repeated after its initial trigger.  If the alarm
      triggers more than once, then this property MUST be specified
      along with the "DURATION" property.

   Format Definition:  This property is defined by the following
      notation:

        repeat  = "REPEAT" repparam ":" integer CRLF
        ;Default is "0", zero.

        repparam   = *(";" other-param)

   Example:  The following is an example of this property for an alarm
      that repeats 4 additional times with a 5 minute delay after the
      initial triggering of the alarm:

        REPEAT:4
        DURATION:PT5M

3.8.6.3.  Trigger

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   Property Name:  TRIGGER

   Purpose:  This property specifies when an alarm will trigger.

   Value Type:  The default value type is DURATION.  The value type can
      be set to a DATE-TIME value type, in which case the value MUST
      specify a UTC formatted DATE-TIME value.

   Property Parameters:  IANA, non-standard, value data type, time zone
      identifier or trigger relationship property parameters can be
      specified on this property.  The trigger relationship property
      parameter MUST only be specified when the value type is
      "DURATION".

   Conformance:  This property MUST be specified in the "VALARM"
      calendar component.

   Description:  This property defines when an alarm will trigger.  The
      default value type is DURATION, specifying a relative time for the
      trigger of the alarm.  The default duration is relative to the
      start of an event or to-do that the alarm is associated with.  The
      duration can be explicitly set to trigger from either the end or
      the start of the associated event or to-do with the "RELATED"
      parameter.  A value of START will set the alarm to trigger off the
      start of the associated event or to-do.  A value of END will set
      the alarm to trigger off the end of the associated event or to-do.

      Either a positive or negative duration may be specified for the
      "TRIGGER" property.  An alarm with a positive duration is
      triggered after the associated start or end of the event or to-do.
      An alarm with a negative duration is triggered before the
      associated start or end of the event or to-do.

      The "RELATED" property parameter is not valid if the value type of
      the property is set to DATE-TIME (i.e., for an absolute date and
      time alarm trigger).  If a value type of DATE-TIME is specified,
      then the property value MUST be specified in the UTC time format.
      If an absolute trigger is specified on an alarm for a recurring
      event or to-do, then the alarm will only trigger for the specified
      absolute date/time, along with any specified repeating instances.

      If the trigger is set relative to START, then the "DTSTART"
      property MUST be present in the associated "VEVENT" or "VTODO"
      calendar component.  If an alarm is specified for an event with
      the trigger set relative to the END, then the "DTEND" property or
      the "DTSTART" and "DURATION " properties MUST be present in the
      associated "VEVENT" calendar component.  If the alarm is specified
      for a to-do with a trigger set relative to the END, then either

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      the "DUE" property or the "DTSTART" and "DURATION " properties
      MUST be present in the associated "VTODO" calendar component.

      Alarms specified in an event or to-do which is defined in terms of
      a DATE value type will be triggered relative to 00:00:00 of the
      user's configured time zone on the specified date, or relative to
      00:00:00 UTC on the specified date if no configured time zone can
      be found for the user.  For example, if "DTSTART" is a DATE value
      set to 19980205 then the duration trigger will be relative to
      19980205T000000 America/New_York for a user configured with the
      America/New_York time zone.

   Format Definition:  This property is defined by the following
      notation:

        trigger    = "TRIGGER" (trigrel / trigabs) CRLF

        trigrel    = *(
                   ;
                   ; the following are OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" "VALUE" "=" "DURATION") /
                   (";" trigrelparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   ) ":"  dur-value

        trigabs    = *(
                   ;
                   ; the following is REQUIRED,
                   ; but MUST NOT occur more than once
                   ;
                   (";" "VALUE" "=" "DATE-TIME") /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   ) ":" date-time

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   Example:  A trigger set 15 minutes prior to the start of the event or
      to-do.

        TRIGGER:-PT15M

      A trigger set 5 minutes after the end of an event or the due date
      of a to-do.

        TRIGGER;RELATED=END:PT5M

      A trigger set to an absolute date/time.

        TRIGGER;VALUE=DATE-TIME:19980101T050000Z

3.8.7.  Change Management Component Properties

   The following properties specify change management information in
   calendar components.

3.8.7.1.  Date/Time Created

   Property Name:  CREATED

   Purpose:  This property specifies the date and time that the calendar
      information was created by the calendar user agent in the calendar
      store.

         Note: This is analogous to the creation date and time for a
         file in the file system.

   Value Type:  DATE-TIME

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  The property can be specified once in "VEVENT", "VTODO"
      or "VJOURNAL" calendar components.  The value MUST be specified as
      a date with UTC time.

   Description:  This property specifies the date and time that the
      calendar information was created by the calendar user agent in the
      calendar store.

   Format Definition:  This property is defined by the following
      notation:

        created    = "CREATED" creaparam ":" date-time CRLF

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        creaparam  = *(";" other-param)

   Example:  The following is an example of this property:

        CREATED:19960329T133000Z

3.8.7.2.  Date/Time Stamp

   Property Name:  DTSTAMP

   Purpose:  In the case of an iCalendar object that specifies a
      "METHOD" property, this property specifies the date and time that
      the instance of the iCalendar object was created.  In the case of
      an iCalendar object that doesn't specify a "METHOD" property, this
      property specifies the date and time that the information
      associated with the calendar component was last revised in the
      calendar store.

   Value Type:  DATE-TIME

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property MUST be included in the "VEVENT",
      "VTODO", "VJOURNAL" or "VFREEBUSY" calendar components.

   Description:  The value MUST be specified in the UTC time format.

      This property is also useful to protocols such as
      [I-D.ietf-calsify-rfc2447bis] that have inherent latency issues
      with the delivery of content.  This property will assist in the
      proper sequencing of messages containing iCalendar objects.

      In the case of an iCalendar object that specifies a "METHOD"
      property, this property differs from the "CREATED" and "LAST-
      MODIFIED" properties.  These two properties are used to specify
      when the particular calendar data in the calendar store was
      created and last modified.  This is different than when the
      iCalendar object representation of the calendar service
      information was created or last modified.

      In the case of an iCalendar object that doesn't specify a "METHOD"
      property, this property is equivalent to the "LAST-MODIFIED"
      property.

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   Format Definition:  This property is defined by the following
      notation:

        dtstamp    = "DTSTAMP" stmparam ":" date-time CRLF

        stmparam   = *(";" other-param)

   Example:

        DTSTAMP:19971210T080000Z

3.8.7.3.  Last Modified

   Property Name:  LAST-MODIFIED

   Purpose:  This property specifies the date and time that the
      information associated with the calendar component was last
      revised in the calendar store.

         Note: This is analogous to the modification date and time for a
         file in the file system.

   Value Type:  DATE-TIME

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  This property can be specified in the "VEVENT",
      "VTODO", "VJOURNAL" or "VTIMEZONE" calendar components.

   Description:  The property value MUST be specified in the UTC time
      format.

   Format Definition:  This property is defined by the following
      notation:

        last-mod   = "LAST-MODIFIED" lstparam ":" date-time CRLF

        lstparam   = *(";" other-param)

   Example:  The following is an example of this property:

        LAST-MODIFIED:19960817T133000Z

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3.8.7.4.  Sequence Number

   Property Name:  SEQUENCE

   Purpose:  This property defines the revision sequence number of the
      calendar component within a sequence of revisions.

   Value Type:  INTEGER

   Property Parameters:  IANA and non-standard property parameters can
      be specified on this property.

   Conformance:  The property can be specified in "VEVENT", "VTODO" or
      "VJOURNAL" calendar component.

   Description:  When a calendar component is created, its sequence
      number is zero (US-ASCII decimal 48).  It is monotonically
      incremented by the "Organizer's" CUA each time the "Organizer"
      makes a significant revision to the calendar component.

      The "Organizer" includes this property in an iCalendar object that
      it sends to an "Attendee" to specify the current version of the
      calendar component.

      The "Attendee" includes this property in an iCalendar object that
      it sends to the "Organizer" to specify the version of the calendar
      component that the "Attendee" is referring to.

      A change to the sequence number is not the mechanism that an
      "Organizer" uses to request a response from the "Attendees".  The
      "RSVP" parameter on the "ATTENDEE" property is used by the
      "Organizer" to indicate that a response from the "Attendees" is
      requested.

      Recurrence instances of a recurring component MAY have different
      sequence numbers.

   Format Definition:  This property is defined by the following
      notation:

        seq = "SEQUENCE" seqparam ":" integer CRLF
        ; Default is "0"

        seqparam   = *(";" other-param)

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   Example:  The following is an example of this property for a calendar
      component that was just created by the "Organizer":

        SEQUENCE:0

      The following is an example of this property for a calendar
      component that has been revised two different times by the
      "Organizer":

        SEQUENCE:2

3.8.8.  Miscellaneous Component Properties

   The following properties specify information about a number of
   miscellaneous features of calendar components.

3.8.8.1.  IANA Properties

   Property Name:  An IANA registered property name

   Value Type:  The default value type is TEXT.  The value type can be
      set to any value type.

   Property Parameters:  Any parameter can be specified on this
      property.

   Description:  This specification allows other properties registered
      with IANA to be specified in any calendar components.  Compliant
      applications are expected to be able to parse these other IANA
      registered properties but can ignore them.

   Format Definition:  This property is defined by the following
      notation:

        iana-prop = iana-token *(";" icalparameter) ":" value CRLF

   Example:  The following are examples of properties that might be
      registered to IANA:

        DRESSCODE:CASUAL

        NON-SMOKING;VALUE=BOOLEAN:TRUE

3.8.8.2.  Non-standard Properties

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   Property Name:  Any property name with a "X-" prefix

   Purpose:  This class of property provides a framework for defining
      non-standard properties.

   Value Type:  The default value type is TEXT.  The value type can be
      set to any value type.

   Property Parameters:  IANA, non-standard and language property
      parameters can be specified on this property.

   Conformance:  This property can be specified in any calendar
      component.

   Description:  The MIME Calendaring and Scheduling Content Type
      provides a "standard mechanism for doing non-standard things".
      This extension support is provided for implementers to "push the
      envelope" on the existing version of the memo.  Extension
      properties are specified by property and/or property parameter
      names that have the prefix text of "X-" (the two character
      sequence: LATIN CAPITAL LETTER X character followed by the HYPHEN-
      MINUS character).  It is recommended that vendors concatenate onto
      this sentinel another short prefix text to identify the vendor.
      This will facilitate readability of the extensions and minimize
      possible collision of names between different vendors.  User
      agents that support this content type are expected to be able to
      parse the extension properties and property parameters but can
      ignore them.

      At present, there is no registration authority for names of
      extension properties and property parameters.  The value type for
      this property is TEXT.  Optionally, the value type can be any of
      the other valid value types.

   Format Definition:  This property is defined by the following
      notation:

        x-prop = x-name *(";" icalparameter) ":" value CRLF

   Example:  The following might be the ABC vendor's extension for an
      audio-clip form of subject property:

        X-ABC-MMSUBJ;VALUE=URI;FMTTYPE=audio/basic:http://www.example.
         org/mysubj.au

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3.8.8.3.  Request Status

   Property Name:  REQUEST-STATUS

   Purpose:  This property defines the status code returned for a
      scheduling request.

   Value Type:  TEXT

   Property Parameters:  IANA, non-standard and language property
      parameters can be specified on this property.

   Conformance:  The property can be specified in "VEVENT", "VTODO",
      "VJOURNAL" or "VFREEBUSY" calendar component.

   Description:  This property is used to return status code information
      related to the processing of an associated iCalendar object.  The
      value type for this property is TEXT.

      The value consists of a short return status component, a longer
      return status description component, and optionally a status-
      specific data component.  The components of the value are
      separated by the SEMICOLON character (US-ASCII decimal 59).

      The short return status is a PERIOD character (US-ASCII decimal
      46) separated pair or 3-tuple of integers.  For example, "3.1" or
      "3.1.1".  The successive levels of integers provide for a
      successive level of status code granularity.

      The following are initial classes for the return status code.
      Individual iCalendar object methods will define specific return
      status codes for these classes.  In addition, other classes for
      the return status code may be defined using the registration
      process defined later in this memo.

   +--------+----------------------------------------------------------+
   | Short  | Longer Return Status Description                         |
   | Return |                                                          |
   | Status |                                                          |
   | Code   |                                                          |
   +--------+----------------------------------------------------------+
   | 1.xx   | Preliminary success.  This class of status code          |
   |        | indicates that the request has been initially processed  |
   |        | but that completion is pending.                          |
   |        |                                                          |

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   | 2.xx   | Successful.  This class of status code indicates that    |
   |        | the request was completed successfuly.  However, the     |
   |        | exact status code can indicate that a fallback has been  |
   |        | taken.                                                   |
   |        |                                                          |
   | 3.xx   | Client Error.  This class of status code indicates that  |
   |        | the request was not successful.  The error is the result |
   |        | of either a syntax or a semantic error in the client     |
   |        | formatted request.  Request should not be retried until  |
   |        | the condition in the request is corrected.               |
   |        |                                                          |
   | 4.xx   | Scheduling Error.  This class of status code indicates   |
   |        | that the request was not successful.  Some sort of error |
   |        | occurred within the calendaring and scheduling service,  |
   |        | not directly related to the request itself.              |
   +--------+----------------------------------------------------------+

   Format Definition:  This property is defined by the following
      notation:

        rstatus    = "REQUEST-STATUS" rstatparam ":"
                     statcode ";" statdesc [";" extdata]

        rstatparam = *(
                   ;
                   ; the following is OPTIONAL,
                   ; but MUST NOT occur more than once
                   ;
                   (";" languageparam) /
                   ;
                   ; the following is OPTIONAL,
                   ; and MAY occur more than once
                   ;
                   (";" other-param)
                   ;
                   )

        statcode   = 1*DIGIT 1*2("." 1*DIGIT)
        ;Hierarchical, numeric return status code

        statdesc   = text
        ;Textual status description

        extdata    = text
        ;Textual exception data. For example, the offending property
        ;name and value or complete property line.

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   Example:  The following are some possible examples of this property.

      The COMMA and SEMICOLON separator characters in the property value
      are BACKSLASH character escaped because they appear in a text
      value.

        REQUEST-STATUS:2.0;Success

        REQUEST-STATUS:3.1;Invalid property value;DTSTART:96-Apr-01

        REQUEST-STATUS:2.8; Success\, repeating event ignored. Scheduled
         as a single event.;RRULE:FREQ=WEEKLY\;INTERVAL=2

        REQUEST-STATUS:4.1;Event conflict. Date/time is busy.

        REQUEST-STATUS:3.7;Invalid calendar user;ATTENDEE:
         mailto:jsmith@example.com

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4.  iCalendar Object Examples

   The following examples are provided as an informational source of
   illustrative iCalendar objects consistent with this content type.

   The following example specifies a three-day conference that begins at
   2:30 P.M. UTC, September 18, 1996 and end at 10:00 P.M. UTC,
   September 20, 1996.

        BEGIN:VCALENDAR
        PRODID:-//xyz Corp//NONSGML PDA Calendar Version 1.0//EN
        VERSION:2.0
        BEGIN:VEVENT
        DTSTAMP:19960704T120000Z
        UID:uid1@example.com
        ORGANIZER:mailto:jsmith@example.com
        DTSTART:19960918T143000Z
        DTEND:19960920T220000Z
        STATUS:CONFIRMED
        CATEGORIES:CONFERENCE
        SUMMARY:Networld+Interop Conference
        DESCRIPTION:Networld+Interop Conference
          and Exhibit\nAtlanta World Congress Center\n
         Atlanta\, Georgia
        END:VEVENT
        END:VCALENDAR

   The following example specifies a group scheduled meeting that begin
   at 8:30 AM EST on March 12, 1998 and end at 9:30 AM EST on March 12,
   1998.  The "Organizer" has scheduled the meeting with one or more
   calendar users in a group.  A time zone specification for Eastern
   United States has been specified.

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        BEGIN:VCALENDAR
        PRODID:-//RDU Software//NONSGML HandCal//EN
        VERSION:2.0
        BEGIN:VTIMEZONE
        TZID:America/New_York
        BEGIN:STANDARD
        DTSTART:19981025T020000
        TZOFFSETFROM:-0400
        TZOFFSETTO:-0500
        TZNAME:EST
        END:STANDARD
        BEGIN:DAYLIGHT
        DTSTART:19990404T020000
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        END:VTIMEZONE
        BEGIN:VEVENT
        DTSTAMP:19980309T231000Z
        UID:guid-1.example.com
        ORGANIZER:mailto:mrbig@example.com
        ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT;CUTYPE=GROUP:
         mailto:employee-A@example.com
        DESCRIPTION:Project XYZ Review Meeting
        CATEGORIES:MEETING
        CLASS:PUBLIC
        CREATED:19980309T130000Z
        SUMMARY:XYZ Project Review
        DTSTART;TZID=America/New_York:19980312T083000
        DTEND;TZID=America/New_York:19980312T093000
        LOCATION:1CP Conference Room 4350
        END:VEVENT
        END:VCALENDAR

   The following is an example of an iCalendar object passed in a MIME
   message with a single body part consisting of a "text/calendar"
   Content Type.

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        TO:jsmith@example.com
        FROM:jdoe@example.com
        MIME-VERSION:1.0
        MESSAGE-ID:<id3@example.com>
        CONTENT-TYPE:text/calendar; method="xyz"; component="VEVENT"

        BEGIN:VCALENDAR
        METHOD:xyz
        VERSION:2.0
        PRODID:-//ABC Corporation//NONSGML My Product//EN
        BEGIN:VEVENT
        DTSTAMP:19970324T120000Z
        SEQUENCE:0
        UID:uid3@example.com
        ORGANIZER:mailto:jdoe@example.com
        ATTENDEE;RSVP=TRUE:mailto:jsmith@example.com
        DTSTART:19970324T123000Z
        DTEND:19970324T210000Z
        CATEGORIES:MEETING,PROJECT
        CLASS:PUBLIC
        SUMMARY:Calendaring Interoperability Planning Meeting
        DESCRIPTION:Discuss how we can test c&s interoperability\n
         using iCalendar and other IETF standards.
        LOCATION:LDB Lobby
        ATTACH;FMTTYPE=application/postscript:ftp://example.com/pub/
         conf/bkgrnd.ps
        END:VEVENT
        END:VCALENDAR

   The following is an example of a to-do due on April 15, 1998.  An
   audio alarm has been specified to remind the calendar user at noon,
   the day before the to-do is expected to be completed and repeat
   hourly, four additional times.  The to-do definition has been
   modified twice since it was initially created.

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        BEGIN:VCALENDAR
        VERSION:2.0
        PRODID:-//ABC Corporation//NONSGML My Product//EN
        BEGIN:VTODO
        DTSTAMP:19980130T134500Z
        SEQUENCE:2
        UID:uid4@example.com
        ORGANIZER:mailto:unclesam@example.com
        ATTENDEE;PARTSTAT=ACCEPTED:mailto:jqpublic@example.com
        DUE:19980415T000000
        STATUS:NEEDS-ACTION
        SUMMARY:Submit Income Taxes
        BEGIN:VALARM
        ACTION:AUDIO
        TRIGGER:19980403T120000Z
        ATTACH;FMTTYPE=audio/basic:http://example.com/pub/audio-
         files/ssbanner.aud
        REPEAT:4
        DURATION:PT1H
        END:VALARM
        END:VTODO
        END:VCALENDAR

   The following is an example of a journal entry.

        BEGIN:VCALENDAR
        VERSION:2.0
        PRODID:-//ABC Corporation//NONSGML My Product//EN
        BEGIN:VJOURNAL
        DTSTAMP:19970324T120000Z
        UID:uid5@example.com
        ORGANIZER:mailto:jsmith@example.com
        STATUS:DRAFT
        CLASS:PUBLIC
        CATEGORIES:Project Report,XYZ,Weekly Meeting
        DESCRIPTION:Project xyz Review Meeting Minutes\n
         Agenda\n1. Review of project version 1.0 requirements.\n2.
          Definition
         of project processes.\n3. Review of project schedule.\n
         Participants: John Smith\, Jane Doe\, Jim Dandy\n-It was
          decided that the requirements need to be signed off by
          product marketing.\n-Project processes were accepted.\n
         -Project schedule needs to account for scheduled holidays
          and employee vacation time. Check with HR for specific
          dates.\n-New schedule will be distributed by Friday.\n-
         Next weeks meeting is cancelled. No meeting until 3/23.
        END:VJOURNAL
        END:VCALENDAR

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   The following is an example of published busy time information.  The
   iCalendar object might be placed in the network resource
   http://www.example.com/calendar/busytime/jsmith.ifb.

        BEGIN:VCALENDAR
        VERSION:2.0
        PRODID:-//RDU Software//NONSGML HandCal//EN
        BEGIN:VFREEBUSY
        ORGANIZER:mailto:jsmith@example.com
        DTSTART:19980313T141711Z
        DTEND:19980410T141711Z
        FREEBUSY:19980314T233000Z/19980315T003000Z
        FREEBUSY:19980316T153000Z/19980316T163000Z
        FREEBUSY:19980318T030000Z/19980318T040000Z
        URL:http://www.example.com/calendar/busytime/jsmith.ifb
        END:VFREEBUSY
        END:VCALENDAR

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5.  Recommended Practices

   These recommended practices should be followed in order to assure
   consistent handling of the following cases for an iCalendar object.

   1.  Content lines longer than 75 octets SHOULD be folded.

   2.  When the combination of the "RRULE" and "RDATE" properties in a
       recurring component produces multiple instances having the same
       start DATE-TIME value, they should be collapsed to, and
       considered as, a single instance.  If the "RDATE" property is
       specified as a PERIOD value the duration of the recurrence
       instance will be the one specified by the "RDATE" property, and
       not the duration of the recurrence instance defined by the
       "DTSTART" property.

   3.  When a calendar user receives multiple requests for the same
       calendar component (e.g., REQUEST for a "VEVENT" calendar
       component) as a result of being on multiple mailing lists
       specified by "ATTENDEE" properties in the request, they SHOULD
       respond to only one of the requests.  The calendar user SHOULD
       also specify (using the "MEMBER" parameter of the "ATTENDEE"
       property) which mailing list they are a member of.

   4.  An implementation can truncate a "SUMMARY" property value to 255
       octets, but MUST NOT truncate the value in the middle of a UTF-8
       multi-octet sequence.

   5.  If seconds of the minute are not supported by an implementation,
       then a value of "00" SHOULD be specified for the seconds
       component in a time value.

   6.  "TZURL" values SHOULD NOT be specified as a file URI type.  This
       URI form can be useful within an organization, but is problematic
       in the Internet.

   7.  Some possible English values for "CATEGORIES" property include
       "ANNIVERSARY", "APPOINTMENT", "BUSINESS", "EDUCATION", "HOLIDAY",
       "MEETING", "MISCELLANEOUS", "NON-WORKING HOURS", "NOT IN OFFICE",
       "PERSONAL", "PHONE CALL", "SICK DAY", "SPECIAL OCCASION",
       "TRAVEL", "VACATION".  Categories can be specified in any
       registered language.

   8.  Some possible English values for "RESOURCES" property include
       "CATERING", "CHAIRS", "COMPUTER PROJECTOR", "EASEL", "OVERHEAD
       PROJECTOR", "SPEAKER PHONE", "TABLE", "TV", "VCR", "VIDEO PHONE",
       "VEHICLE".  Resources can be specified in any registered
       language.

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6.  Internationalization Considerations

   Applications MUST generate iCalendar stream in the UTF-8 charset and
   MUST accept iCalendar stream in the UTF-8 or US-ASCII charset.

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7.  Security Considerations

   Because calendaring and scheduling information is very privacy-
   sensitive, the protocol used for the transmission of calendaring and
   scheduling information should have capabilities to protect the
   information from possible threats, such as eavesdropping, replay,
   message insertion, deletion, modification and man-in-the-middle
   attacks.

   As this document only defines the data format and media type of text/
   calendar that is independent of any calendar service or protocol, it
   is up to the actual protocol specifications such as iTIP
   [I-D.ietf-calsify-2446bis], iMIP [I-D.ietf-calsify-rfc2447bis], and
   CalDAV [RFC4791] to describe the threats that the above attacks
   present, as well as ways in which to mitigate them.

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8.  IANA Considerations

8.1.  iCalendar Media Type Registration

   The Calendaring and Scheduling Core Object Specification is intended
   for use as a MIME content type.

   To: ietf-types@iana.org
   Subject: Registration of media type text/calendar

   Type name:  text

   Subtype name:  calendar

   Required parameters:  none

   Optional parameters:  charset, method, component and optinfo

      The "charset" parameter is defined in [RFC2046] for subtypes of
      the "text" media type.  It is used to indicate the charset used in
      the body part.  The charset supported by this revision of
      iCalendar is UTF-8.  The use of any other charset is deprecated by
      this revision of iCalendar; however note that this revision
      requires that compliant applications MUST accept iCalendar streams
      using either the UTF-8 or US-ASCII charset.

      The "method" parameter is used to convey the iCalendar object
      method or transaction semantics for the calendaring and scheduling
      information.  It also is an identifier for the restricted set of
      properties and values that the iCalendar object consists of.  The
      parameter is to be used as a guide for applications interpreting
      the information contained within the body part.  It SHOULD NOT be
      used to exclude or require particular pieces of information unless
      the identified method definition specifically calls for this
      behavior.  Unless specifically forbidden by a particular method
      definition, a text/calendar content type can contain any set of
      properties permitted by the Calendaring and Scheduling Core Object
      Specification.  The "method" parameter MUST be specified and MUST
      be set to the same value as the "METHOD" component property of the
      iCalendar objects of the iCalendar stream if and only if the
      iCalendar objects in the iCalendar stream all have a "METHOD"
      component property set to the same value.

      The value for the "method" parameter is defined as follows:

        method  = 1*(ALPHA / DIGIT / "-")
        ; IANA registered iCalendar object method

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      The "component" parameter conveys the type of iCalendar calendar
      component within the body part.  If the iCalendar object contains
      more than one calendar component type, then multiple component
      parameters MUST be specified.

      The value for the "component" parameter is defined as follows:

        component = "VEVENT"
                  / "VTODO"
                  / "VJOURNAL"
                  / "VFREEBUSY"
                  / "VTIMEZONE"
                  / iana-token
                  / x-name

      The "optinfo" parameter conveys optional information about the
      iCalendar object within the body part.  This parameter can only
      specify semantics already specified by the iCalendar object and
      that can be otherwise determined by parsing the body part.  In
      addition, the optional information specified by this parameter
      MUST be consistent with that information specified by the
      iCalendar object.  For example, it can be used to convey the
      "Attendee" response status to a meeting request.  The parameter
      value consists of a string value.

      The parameter can be specified multiple times.

      The value for the "optinfo" parameter is defined as follows:

        optinfo    = infovalue / qinfovalue

        infovalue  = iana-token / x-name

        qinfovalue = DQUOTE (infovalue) DQUOTE

   Encoding considerations:  This media type can contain 8bit
      characters, so the use of quoted-printable or base64 MIME Content-
      Transfer-Encodings might be necessary when iCalendar objects are
      transferred across protocols restricted to the 7bit repertoire.
      Note that a text valued property in the content entity can also
      have content encoding of special characters using a BACKSLASH
      character (US-ASCII decimal 92) escapement technique.  This means
      that content values can end up encoded twice.

   Security considerations:  See Section 7.

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   Interoperability considerations:  This media type is intended to
      define a common format for conveying calendaring and scheduling
      information between different systems.  It is heavily based on the
      earlier [VCAL] industry specification.

   Published specification:  This specification.

   Applications which use this media type:  This media type is designed
      for widespread use by Internet calendaring and scheduling
      applications.  In addition, applications in the workflow and
      document management area might find this content-type applicable.
      The iTIP [I-D.ietf-calsify-2446bis], iMIP
      [I-D.ietf-calsify-rfc2447bis] and CalDAV [RFC4791] Internet
      protocols directly use this media type also.

   Additional information:

      Magic number(s):  None.

      File extension(s):  The file extension of "ics" is to be used to
         designate a file containing (an arbitrary set of) calendaring
         and scheduling information consistent with this MIME content
         type.

         The file extension of "ifb" is to be used to designate a file
         containing free or busy time information consistent with this
         MIME content type.

      Macintosh file type code(s):  The file type code of "iCal" is to
         be used in Apple MacIntosh operating system environments to
         designate a file containing calendaring and scheduling
         information consistent with this MIME media type.

         The file type code of "iFBf" is to be used in Apple MacIntosh
         operating system environments to designate a file containing
         free or busy time information consistent with this MIME media
         type.

   Person & email address to contact for further information:  See the
      "Author's Address" section of this document.

   Intended usage:  COMMON

   Restrictions on usage:  There are no restrictions on where this media
      type can be used.

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   Author:  See the "Author's Address" section of this document.

   Change controller:  IETF

8.2.  New iCalendar Elements Registration

   This section defines the process to register new or modified
   iCalendar elements, that is, components, properties, parameters,
   value data types, and values, with IANA.

8.2.1.  iCalendar Elements Registration Procedure

   The IETF will create a mailing list, icalendar@ietf.org [2], which
   can be used for public discussion of iCalendar elements proposals
   prior to registration.  Use of the mailing list is strongly
   encouraged.  The IESG will appoint a designated expert who will
   monitor the icalendar@ietf.org [2] mailing list and review
   registrations.

   Registration of new iCalendar elements MUST be reviewed by the
   designated expert and published in an RFC.  A Standard Tracks RFC is
   REQUIRED for the regisration of new value data types that modify
   existing properties, as well as for the registration of participation
   statuses values to be used in "VEVENT" calendar components.  A
   Standard Tracks RFC is also REQUIRED for registration of iCalendar
   elements that modify iCalendar elements previously documented in a
   Standard Tracks RFC.

   The registration procedure begins when a completed registration
   template, defined in the sections below, is sent to
   icalendar@ietf.org [2] and iana@iana.org [3].  The designated expert
   is expected to tell IANA and the submitter of the registration within
   two weeks whether the registration is approved, approved with minor
   changes, or rejected with cause.  When a registration is rejected
   with cause, it can be re-submitted if the concerns listed in the
   cause are addressed.  Decisions made by the designated expert can be
   appealed to the IESG Applications Area Director, then to the IESG.
   They follow the normal appeals procedure for IESG decisions.

8.2.2.  Registration Template for Components

   A component is defined by completing the following template.

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      Component name:  The name of the component.

      Purpose:  The purpose of the component.  Give a short but clear
         description.

      Format definition:  The ABNF for the component definition needs to
         be specified.

      Description:  Any special notes about the component, how it is to
         be used, etc.

      Example(s):  One or more examples of instances of the component
         needs to be specified.

8.2.3.  Registration Template for Properties

   A property is defined by completing the following template.

      Property name:  The name of the property.

      Purpose:  The purpose of the property.  Give a short but clear
         description.

      Value type:  Any of the valid value types for the property value
         needs to be specified.  The default value type also needs to be
         specified.

      Property parameters:  Any of the valid property parameters for the
         property MUST be specified.

      Conformance:  The calendar components that the property can appear
         in MUST be specified.

      Description:  Any special notes about the property, how it is to
         be used, etc.

      Format definition:  The ABNF for the property definition needs to
         be specified.

      Example(s):  One or more examples of instances of the property
         needs to be specified.

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8.2.4.  Registration Template for Parameters

   A parameter is defined by completing the following template.

      Parameter name:  The name of the parameter.

      Purpose:  The purpose of the parameter.  Give a short but clear
         description.

      Format definition:  The ABNF for the parameter definition needs to
         be specified.

      Description:  Any special notes about the parameter, how it is to
         be used, etc.

      Example(s):  One or more examples of instances of the parameter
         needs to be specified.

8.2.5.  Registration Template for Value Data Types

   A value data type is defined by completing the following template.

      Value name:  The name of the value type.

      Purpose:  The purpose of the value type.  Give a short but clear
         description.

      Format definition:  The ABNF for the value type definition needs
         to be specified.

      Description:  Any special notes about the value type, how it is to
         be used, etc.

      Example(s):  One or more examples of instances of the value type
         needs to be specified.

8.2.6.  Registration Template for Values

   A value is defined by completing the following template.

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      Value:  The value literal.

      Purpose:  The purpose of the value.  Give a short but clear
         description.

      Conformance:  The calendar properties and/or parameters that can
         take this value needs to be specified.

      Example(s):  One or more examples of instances of the value needs
         to be specified.

   The following is a fictitious example of a registration of an
   iCalendar value:

      Value:  TOP-SECRET

      Purpose:  This value is used to specify the access classification
         of top-secret calendar components.

      Conformance:  This value can be used with the "CLASS" property.

      Example(s):  The following is an example of this value used with
         the "CLASS" property:

      CLASS:TOP-SECRET

8.3.  Initial iCalendar Elements Registries

   The IANA is requested to create and maintain the following registries
   for iCalendar elements with pointers to appropriate reference
   documents.

8.3.1.  Components Registry

   The following table is to be used to initialize the components
   registry.

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             +-----------+---------+------------------------+
             | Component | Status  | Reference              |
             +-----------+---------+------------------------+
             | VCALENDAR | Current | RFCXXXX, Section 3.4   |
             |           |         |                        |
             | VEVENT    | Current | RFCXXXX, Section 3.6.1 |
             |           |         |                        |
             | VTODO     | Current | RFCXXXX, Section 3.6.2 |
             |           |         |                        |
             | VJOURNAL  | Current | RFCXXXX, Section 3.6.3 |
             |           |         |                        |
             | VFREEBUSY | Current | RFCXXXX, Section 3.6.4 |
             |           |         |                        |
             | VTIMEZONE | Current | RFCXXXX, Section 3.6.5 |
             |           |         |                        |
             | VALARM    | Current | RFCXXXX, Section 3.6.6 |
             |           |         |                        |
             | STANDARD  | Current | RFCXXXX, Section 3.6.5 |
             |           |         |                        |
             | DAYLIGHT  | Current | RFCXXXX, Section 3.6.5 |
             +-----------+---------+------------------------+

8.3.2.  Properties Registry

   The following table is to be used to initialize the properties
   registry.

       +------------------+------------+---------------------------+
       | Property         | Status     | Reference                 |
       +------------------+------------+---------------------------+
       | CALSCALE         | Current    | RFCXXXX, Section 3.7.1    |
       |                  |            |                           |
       | METHOD           | Current    | RFCXXXX, Section 3.7.2    |
       |                  |            |                           |
       | PRODID           | Current    | RFCXXXX, Section 3.7.3    |
       |                  |            |                           |
       | VERSION          | Current    | RFCXXXX, Section 3.7.4    |
       |                  |            |                           |
       | ATTACH           | Current    | RFCXXXX, Section 3.8.1.1  |
       |                  |            |                           |
       | CATEGORIES       | Current    | RFCXXXX, Section 3.8.1.2  |
       |                  |            |                           |
       | CLASS            | Current    | RFCXXXX, Section 3.8.1.3  |
       |                  |            |                           |
       | COMMENT          | Current    | RFCXXXX, Section 3.8.1.4  |
       |                  |            |                           |
       | DESCRIPTION      | Current    | RFCXXXX, Section 3.8.1.5  |
       |                  |            |                           |

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       | GEO              | Current    | RFCXXXX, Section 3.8.1.6  |
       |                  |            |                           |
       | LOCATION         | Current    | RFCXXXX, Section 3.8.1.7  |
       |                  |            |                           |
       | PERCENT-COMPLETE | Current    | RFCXXXX, Section 3.8.1.8  |
       |                  |            |                           |
       | PRIORITY         | Current    | RFCXXXX, Section 3.8.1.9  |
       |                  |            |                           |
       | RESOURCES        | Current    | RFCXXXX, Section 3.8.1.10 |
       |                  |            |                           |
       | STATUS           | Current    | RFCXXXX, Section 3.8.1.11 |
       |                  |            |                           |
       | SUMMARY          | Current    | RFCXXXX, Section 3.8.1.12 |
       |                  |            |                           |
       | COMPLETED        | Current    | RFCXXXX, Section 3.8.2.1  |
       |                  |            |                           |
       | DTEND            | Current    | RFCXXXX, Section 3.8.2.2  |
       |                  |            |                           |
       | DUE              | Current    | RFCXXXX, Section 3.8.2.3  |
       |                  |            |                           |
       | DTSTART          | Current    | RFCXXXX, Section 3.8.2.4  |
       |                  |            |                           |
       | DURATION         | Current    | RFCXXXX, Section 3.8.2.5  |
       |                  |            |                           |
       | FREEBUSY         | Current    | RFCXXXX, Section 3.8.2.6  |
       |                  |            |                           |
       | TRANSP           | Current    | RFCXXXX, Section 3.8.2.7  |
       |                  |            |                           |
       | TZID             | Current    | RFCXXXX, Section 3.8.3.1  |
       |                  |            |                           |
       | TZNAME           | Current    | RFCXXXX, Section 3.8.3.2  |
       |                  |            |                           |
       | TZOFFSETFROM     | Current    | RFCXXXX, Section 3.8.3.3  |
       |                  |            |                           |
       | TZOFFSETTO       | Current    | RFCXXXX, Section 3.8.3.4  |
       |                  |            |                           |
       | TZURL            | Current    | RFCXXXX, Section 3.8.3.5  |
       |                  |            |                           |
       | ATTENDEE         | Current    | RFCXXXX, Section 3.8.4.1  |
       |                  |            |                           |
       | CONTACT          | Current    | RFCXXXX, Section 3.8.4.2  |
       |                  |            |                           |
       | ORGANIZER        | Current    | RFCXXXX, Section 3.8.4.3  |
       |                  |            |                           |
       | RECURRENCE-ID    | Current    | RFCXXXX, Section 3.8.4.4  |
       |                  |            |                           |
       | RELATED-TO       | Current    | RFCXXXX, Section 3.8.4.5  |
       |                  |            |                           |

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       | URL              | Current    | RFCXXXX, Section 3.8.4.6  |
       |                  |            |                           |
       | UID              | Current    | RFCXXXX, Section 3.8.4.7  |
       |                  |            |                           |
       | EXDATE           | Current    | RFCXXXX, Section 3.8.5.1  |
       |                  |            |                           |
       | EXRULE           | Deprecated | RFC2445, Section 4.8.5.2  |
       |                  |            |                           |
       | RDATE            | Current    | RFCXXXX, Section 3.8.5.2  |
       |                  |            |                           |
       | RRULE            | Current    | RFCXXXX, Section 3.8.5.3  |
       |                  |            |                           |
       | ACTION           | Current    | RFCXXXX, Section 3.8.6.1  |
       |                  |            |                           |
       | REPEAT           | Current    | RFCXXXX, Section 3.8.6.2  |
       |                  |            |                           |
       | TRIGGER          | Current    | RFCXXXX, Section 3.8.6.3  |
       |                  |            |                           |
       | CREATED          | Current    | RFCXXXX, Section 3.8.7.1  |
       |                  |            |                           |
       | DTSTAMP          | Current    | RFCXXXX, Section 3.8.7.2  |
       |                  |            |                           |
       | LAST-MODIFIED    | Current    | RFCXXXX, Section 3.8.7.3  |
       |                  |            |                           |
       | SEQUENCE         | Current    | RFCXXXX, Section 3.8.7.4  |
       |                  |            |                           |
       | REQUEST-STATUS   | Current    | RFCXXXX, Section 3.8.8.3  |
       +------------------+------------+---------------------------+

8.3.3.  Parameters Registry

   The following table is to be used to initialize the parameters
   registry.

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          +----------------+---------+-------------------------+
          | Parameter      | Status  | Reference               |
          +----------------+---------+-------------------------+
          | ALTREP         | Current | RFCXXXX, Section 3.2.1  |
          |                |         |                         |
          | CN             | Current | RFCXXXX, Section 3.2.2  |
          |                |         |                         |
          | CUTYPE         | Current | RFCXXXX, Section 3.2.3  |
          |                |         |                         |
          | DELEGATED-FROM | Current | RFCXXXX, Section 3.2.4  |
          |                |         |                         |
          | DELEGATED-TO   | Current | RFCXXXX, Section 3.2.5  |
          |                |         |                         |
          | DIR            | Current | RFCXXXX, Section 3.2.6  |
          |                |         |                         |
          | ENCODING       | Current | RFCXXXX, Section 3.2.7  |
          |                |         |                         |
          | FMTTYPE        | Current | RFCXXXX, Section 3.2.8  |
          |                |         |                         |
          | FBTYPE         | Current | RFCXXXX, Section 3.2.9  |
          |                |         |                         |
          | LANGUAGE       | Current | RFCXXXX, Section 3.2.10 |
          |                |         |                         |
          | MEMBER         | Current | RFCXXXX, Section 3.2.11 |
          |                |         |                         |
          | PARTSTAT       | Current | RFCXXXX, Section 3.2.12 |
          |                |         |                         |
          | RANGE          | Current | RFCXXXX, Section 3.2.13 |
          |                |         |                         |
          | RELATED        | Current | RFCXXXX, Section 3.2.14 |
          |                |         |                         |
          | RELTYPE        | Current | RFCXXXX, Section 3.2.15 |
          |                |         |                         |
          | ROLE           | Current | RFCXXXX, Section 3.2.16 |
          |                |         |                         |
          | RSVP           | Current | RFCXXXX, Section 3.2.17 |
          |                |         |                         |
          | SENT-BY        | Current | RFCXXXX, Section 3.2.18 |
          |                |         |                         |
          | TZID           | Current | RFCXXXX, Section 3.2.19 |
          |                |         |                         |
          | VALUE          | Current | RFCXXXX, Section 3.2.20 |
          +----------------+---------+-------------------------+

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8.3.4.  Value Data Types Registry

   The following table is to be used to initialize the value data types
   registry.

          +-----------------+---------+-------------------------+
          | Value Data Type | Status  | Reference               |
          +-----------------+---------+-------------------------+
          | BINARY          | Current | RFCXXXX, Section 3.3.1  |
          |                 |         |                         |
          | BOOLEAN         | Current | RFCXXXX, Section 3.3.2  |
          |                 |         |                         |
          | CAL-ADDRESS     | Current | RFCXXXX, Section 3.3.3  |
          |                 |         |                         |
          | DATE            | Current | RFCXXXX, Section 3.3.4  |
          |                 |         |                         |
          | DATE-TIME       | Current | RFCXXXX, Section 3.3.5  |
          |                 |         |                         |
          | DURATION        | Current | RFCXXXX, Section 3.3.6  |
          |                 |         |                         |
          | FLOAT           | Current | RFCXXXX, Section 3.3.7  |
          |                 |         |                         |
          | INTEGER         | Current | RFCXXXX, Section 3.3.8  |
          |                 |         |                         |
          | PERIOD          | Current | RFCXXXX, Section 3.3.9  |
          |                 |         |                         |
          | RECUR           | Current | RFCXXXX, Section 3.3.10 |
          |                 |         |                         |
          | TEXT            | Current | RFCXXXX, Section 3.3.11 |
          |                 |         |                         |
          | TIME            | Current | RFCXXXX, Section 3.3.12 |
          |                 |         |                         |
          | URI             | Current | RFCXXXX, Section 3.3.13 |
          |                 |         |                         |
          | UTC-OFFSET      | Current | RFCXXXX, Section 3.3.14 |
          +-----------------+---------+-------------------------+

8.3.5.  Calendar User Types Registry

   The following table is to be used to initialize the calendar user
   types registry.

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         +--------------------+---------+------------------------+
         | Calendar User Type | Status  | Reference              |
         +--------------------+---------+------------------------+
         | INDIVIDUAL         | Current | RFCXXXX, Section 3.2.3 |
         |                    |         |                        |
         | GROUP              | Current | RFCXXXX, Section 3.2.3 |
         |                    |         |                        |
         | RESOURCE           | Current | RFCXXXX, Section 3.2.3 |
         |                    |         |                        |
         | ROOM               | Current | RFCXXXX, Section 3.2.3 |
         |                    |         |                        |
         | UNKNOWN            | Current | RFCXXXX, Section 3.2.3 |
         +--------------------+---------+------------------------+

8.3.6.  Free/Busy Time Types Registry

   The following table is to be used to initialize the free/busy time
   types registry.

        +---------------------+---------+------------------------+
        | Free/Busy Time Type | Status  | Reference              |
        +---------------------+---------+------------------------+
        | FREE                | Current | RFCXXXX, Section 3.2.9 |
        |                     |         |                        |
        | BUSY                | Current | RFCXXXX, Section 3.2.9 |
        |                     |         |                        |
        | BUSY-UNAVAILABLE    | Current | RFCXXXX, Section 3.2.9 |
        |                     |         |                        |
        | BUSY-TENTATIVE      | Current | RFCXXXX, Section 3.2.9 |
        +---------------------+---------+------------------------+

8.3.7.  Participation Statuses Registry

   The following table is to be used to initialize the participation
   statuses registry.

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        +--------------------+---------+-------------------------+
        | Participant Status | Status  | Reference               |
        +--------------------+---------+-------------------------+
        | NEEDS-ACTION       | Current | RFCXXXX, Section 3.2.12 |
        |                    |         |                         |
        | ACCEPTED           | Current | RFCXXXX, Section 3.2.12 |
        |                    |         |                         |
        | DECLINED           | Current | RFCXXXX, Section 3.2.12 |
        |                    |         |                         |
        | TENTATIVE          | Current | RFCXXXX, Section 3.2.12 |
        |                    |         |                         |
        | DELEGATED          | Current | RFCXXXX, Section 3.2.12 |
        |                    |         |                         |
        | COMPLETED          | Current | RFCXXXX, Section 3.2.12 |
        |                    |         |                         |
        | IN-PROCESS         | Current | RFCXXXX, Section 3.2.12 |
        +--------------------+---------+-------------------------+

8.3.8.  Relationship Types Registry

   The following table is to be used to initialize the property
   parameters registry.

         +-------------------+---------+-------------------------+
         | Relationship Type | Status  | Reference               |
         +-------------------+---------+-------------------------+
         | CHILD             | Current | RFCXXXX, Section 3.2.15 |
         |                   |         |                         |
         | PARENT            | Current | RFCXXXX, Section 3.2.15 |
         |                   |         |                         |
         | SIBLING           | Current | RFCXXXX, Section 3.2.15 |
         +-------------------+---------+-------------------------+

8.3.9.  Participation Roles Registry

   The following table is to be used to initialize the participation
   roles registry.

          +-----------------+---------+-------------------------+
          | Role Type       | Status  | Reference               |
          +-----------------+---------+-------------------------+
          | CHAIR           | Current | RFCXXXX, Section 3.2.16 |
          |                 |         |                         |
          | REQ-PARTICIPANT | Current | RFCXXXX, Section 3.2.16 |
          |                 |         |                         |
          | OPT-PARTICIPANT | Current | RFCXXXX, Section 3.2.16 |
          |                 |         |                         |

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          | NON-PARTICIPANT | Current | RFCXXXX, Section 3.2.16 |
          +-----------------+---------+-------------------------+

8.3.10.  Actions Registry

   The following table is to be used to initialize the actions registry.

           +-----------+------------+--------------------------+
           | Action    | Status     | Reference                |
           +-----------+------------+--------------------------+
           | AUDIO     | Current    | RFCXXXX, Section 3.8.6.1 |
           |           |            |                          |
           | DISPLAY   | Current    | RFCXXXX, Section 3.8.6.1 |
           |           |            |                          |
           | EMAIL     | Current    | RFCXXXX, Section 3.8.6.1 |
           |           |            |                          |
           | PROCEDURE | Deprecated | RFC2445, Section 4.8.6.1 |
           +-----------+------------+--------------------------+

8.3.11.  Classifications Registry

   The following table is to be used to initialize the classifications
   registry.

          +----------------+---------+--------------------------+
          | Classification | Status  | Reference                |
          +----------------+---------+--------------------------+
          | PUBLIC         | Current | RFCXXXX, Section 3.8.1.3 |
          |                |         |                          |
          | PRIVATE        | Current | RFCXXXX, Section 3.8.1.3 |
          |                |         |                          |
          | CONFIDENTIAL   | Current | RFCXXXX, Section 3.8.1.3 |
          +----------------+---------+--------------------------+

8.3.12.  Methods Registry

   No values are defined in this document for the "METHOD" property.

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9.  Acknowledgements

   The editor of this document wish to thank Frank Dawson and Derik
   Stenerson, the original authors of RFC2445, as well as the following
   individuals who have participated in the drafting, review and
   discussion of this memo:

   Joe Abley, Hervey Allen, Steve Allen, Jay Batson, Oliver Block,
   Stephane Bortzmeyer, Chris Bryant, Tantek Celik, Mark Crispin, Cyrus
   Daboo, Mike Douglass, Andrew N. Dowden, Lisa Dusseault, Lars Eggert,
   Gren Eliot, Pasi Eronen, Ben Fortuna, Ned Freed, Neal Gafter, Ted
   Hardie, Tim Hare, Jeffrey Harris, Helge Hess, Paul B. Hill, Thomas
   Hnetila, Russ Housley, Leif Johansson, Ciny Joy, Bruce Kahn, Reinhold
   Kainhofer, Martin Kiff, Patrice Lapierre, Eliot Lear, Michiel van
   Leeuwen, Jonathan Lennox, Jeff McCullough, Bill McQuillan, Alexey
   Melnikov, Aki Niemi, John W. Noerenberg II, Chuck Norris, Mark
   Paterson, Simon Pilette, Arnaud Quillaud, Robert Ransdell, Julian F.
   Reschke, Caleb Richardson, Sam Roberts, Dan Romascanu, Mike Samuel,
   George Sexton, Nigel Swinson, Clint Talbert, Simon Vaillancourt,
   Magnus Westerlund, and Sandy Wills.

   The editor would also like to thank the Calendaring and Scheduling
   Consortium for advice with this specification, and for organizing
   interoperability testing events to help refine it.

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10.  References

10.1.  Normative References

   [ISO.8601.2004]                International Organization for
                                  Standardization, "Data elements and
                                  interchange formats -- Information
                                  interchange -- Representation of dates
                                  and times", 2004.

   [ISO.9070.1991]                International Organization for
                                  Standardization, "Information
                                  Technology_SGML Support Facilities --
                                  Registration Procedures for Public
                                  Text Owner Identifiers, Second
                                  Edition", April 1991.

   [RFC2045]                      Freed, N. and N. Borenstein,
                                  "Multipurpose Internet Mail Extensions
                                  (MIME) Part One: Format of Internet
                                  Message Bodies", RFC 2045,
                                  November 1996.

   [RFC2046]                      Freed, N. and N. Borenstein,
                                  "Multipurpose Internet Mail Extensions
                                  (MIME) Part Two: Media Types",
                                  RFC 2046, November 1996.

   [RFC2119]                      Bradner, S., "Key words for use in
                                  RFCs to Indicate Requirement Levels",
                                  BCP 14, RFC 2119, March 1997.

   [RFC2368]                      Hoffman, P., Masinter, L., and J.
                                  Zawinski, "The mailto URL scheme",
                                  RFC 2368, July 1998.

   [RFC3629]                      Yergeau, F., "UTF-8, a transformation
                                  format of ISO 10646", STD 63,
                                  RFC 3629, November 2003.

   [RFC3986]                      Berners-Lee, T., Fielding, R., and L.
                                  Masinter, "Uniform Resource Identifier
                                  (URI): Generic Syntax", STD 66,
                                  RFC 3986, January 2005.

   [RFC4288]                      Freed, N. and J. Klensin, "Media Type
                                  Specifications and Registration
                                  Procedures", BCP 13, RFC 4288,

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                                  December 2005.

   [RFC4646]                      Phillips, A. and M. Davis, "Tags for
                                  Identifying Languages", BCP 47,
                                  RFC 4646, September 2006.

   [RFC4648]                      Josefsson, S., "The Base16, Base32,
                                  and Base64 Data Encodings", RFC 4648,
                                  October 2006.

   [RFC5234]                      Crocker, D. and P. Overell, "Augmented
                                  BNF for Syntax Specifications: ABNF",
                                  STD 68, RFC 5234, January 2008.

10.2.  Informative References

   [I-D.ietf-calsify-2446bis]     Daboo, C., "iCalendar Transport-
                                  Independent Interoperability Protocol
                                  (iTIP)", draft-ietf-calsify-2446bis-09
                                  (work in progress), April 2009.

   [I-D.ietf-calsify-rfc2447bis]  Melnikov, A., "iCalendar Message-Based
                                  Interoperability Protocol(iMIP)",
                                  draft-ietf-calsify-rfc2447bis-05 (work
                                  in progress), June 2008.

   [RFC1738]                      Berners-Lee, T., Masinter, L., and M.
                                  McCahill, "Uniform Resource Locators
                                  (URL)", RFC 1738, December 1994.

   [RFC2392]                      Levinson, E., "Content-ID and
                                  Message-ID Uniform Resource Locators",
                                  RFC 2392, August 1998.

   [RFC2397]                      Masinter, L., "The "data" URL scheme",
                                  RFC 2397, August 1998.

   [RFC2425]                      Howes, T., Smith, M., and F. Dawson,
                                  "A MIME Content-Type for Directory
                                  Information", RFC 2425,
                                  September 1998.

   [RFC2426]                      Dawson, F. and T. Howes, "vCard MIME
                                  Directory Profile", RFC 2426,
                                  September 1998.

   [RFC2616]                      Fielding, R., Gettys, J., Mogul, J.,
                                  Frystyk, H., Masinter, L., Leach, P.,

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                                  and T. Berners-Lee, "Hypertext
                                  Transfer Protocol -- HTTP/1.1",
                                  RFC 2616, June 1999.

   [RFC2818]                      Rescorla, E., "HTTP Over TLS",
                                  RFC 2818, May 2000.

   [RFC4516]                      Smith, M. and T. Howes, "Lightweight
                                  Directory Access Protocol (LDAP):
                                  Uniform Resource Locator", RFC 4516,
                                  June 2006.

   [RFC4791]                      Daboo, C., Desruisseaux, B., and L.
                                  Dusseault, "Calendaring Extensions to
                                  WebDAV (CalDAV)", RFC 4791,
                                  March 2007.

   [TZDB]                         Eggert, P. and A. Olson, "Sources for
                                  Time Zone and Daylight Saving Time
                                  Data", January 2007, <http://
                                  www.twinsun.com/tz/tz-link.htm>.

                                  [Note to RFC Editor: Change "A. Olson"
                                  to "A.D. Olson".]

   [VCAL]                         Internet Mail Consortium, "vCalendar:
                                  The Electronic Calendaring and
                                  Scheduling Exchange Format",
                                  September 1996,
                                  <http://www.imc.org/pdi/vcal-10.txt>.

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URIs

   [1]  <mailto:ietf-calsify@osafoundation.org>

   [2]  <mailto:icalendar@ietf.org>

   [3]  <mailto:iana@iana.org>

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Appendix A.  Differences from RFC 2445

   This appendix contains a list of changes that have been made in the
   Internet Calendaring and Scheduling Core Object Specification from
   RFC 2445.

A.1.  New restrictions

   1.  The "DTSTART" property SHOULD be synchronized with the recurrence
       rule, if specified.

   2.  The "RRULE" property SHOULD NOT occur more than once in a
       component.

   3.  The BYHOUR, BYMINUTE and BYSECOND rule parts MUST NOT be
       specified in the "RRULE" property when the "DTSTART" property is
       specified as a DATE value.

   4.  The value type of the "DTEND" or "DUE" properties MUST match the
       value type of "DTSTART" property.

   5.  The "DURATION" property can no longer appear in "VFREEBUSY"
       components.

A.2.  Restrictions removed

   1.  The "DTSTART" and "DTEND" properties are no longer required to be
       specified as date with local time and time zone reference when
       used with a recurrence rule.

A.3.  Deprecated features

   1.  The "EXRULE" property can no longer be specified in a component.

   2.  The "THISANDPRIOR" value can no longer be used with the "RANGE"
       parameter.

   3.  The "PROCEDURE" value can no longer be used with the "ACTION"
       property.

   4.  The value type RECUR no longer allow multiple values to be
       specified by a COMMA (US-ASCII decimal 44) character separated
       list of values.

   5.  x-name rule parts can no longer be specified in properties of
       RECUR value type (e.g., "RRULE"). x-param can be used on RECUR
       value type properties instead.

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Appendix B.  Change Log (to be removed by RFC Editor prior to
             publication)

B.1.  Changes in -10

   A detailed list of changes is available at the following page:
   http://tools.ietf.org/wg/calsify/draft-ietf-calsify-rfc2445bis/
   draft-ietf-calsify-rfc2445bis-10.changes.html.

   a.  Addressed IESG evaluation comments and discusses.

   b.  Clarified that the "RECURRENCE-ID" property MUST have the same
       value type as the "DTSTART" property contained within the
       recurring component and MUST be specified as a date with local
       time if and only if the "DTSTART" property contained within the
       recurring component is specified as a date with local time.

B.2.  Changes in -09

   A detailed list of changes is available at the following page:
   http://tools.ietf.org/wg/calsify/draft-ietf-calsify-rfc2445bis/
   draft-ietf-calsify-rfc2445bis-09.changes.html.

   a.  Issue 60: Clarified that multi-valued properties MUST NOT be used
       to specify multiple language variants of the same value.

   b.  Issue 67: Forbid the use of the "DURATION" property in
       "VFREEBUSY" components.

   c.  AD-Issue 1: Added note on most commonly used URI schemes for the
       "ALTREP" parameter.

   d.  AD-Issue 2: Added recommendation on the URI schemes to use for
       the "DIR" parameter.

   e.  AD-Issue 4: Added recommendation for calendar applications that
       support importing iCalendar objects.

   f.  iTIP-APPS-Issue 1: Allowed "DTSTART" to be OPTIONAL for iTIP.

   g.  iTIP-APPS-Issue 2: Fixed time zone example.

   h.  iTIP-APPS-Issue 3: Clarified that recurrence instances MAY have
       different sequence numbers.

   i.  iTIP-APPS-Issue 4: Clarified description of the "INTERVAL" rule
       part.

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   j.  Modified TSAFE-CHAR to allow HTAB (US-ASCII decimal 9) in TEXT
       values.

   k.  Few editorial changes.

   l.  Added names to the Acknowledgments section.

B.3.  Changes in -08

   A detailed list of changes is available at the following page:
   http://tools.ietf.org/wg/calsify/draft-ietf-calsify-rfc2445bis/
   draft-ietf-calsify-rfc2445bis-08.changes.html.

   a.  Issue 48: Revert the change to deprecate the "RANGE" parameter.
       Only the value "THISANDPRIOR" is deprecated.

   b.  Issue 81: BYSETPOS: Clarify that "a set" starts at the beginning
       of the interval defined by the FREQ rule part.

   c.  Chair Review: Changed requirement to handle unrecognized CUTYPE
       values.

   d.  Chair Review: Changed requirement to handle unrecognized VALUE
       data types.

   e.  Chair Review: Removed requirements for "DELEGATED-TO" and
       "DELEGATED-FROM" to be specified as mailto URI.

   f.  Chair Review: Added note about alarms from untrusted sources.

   g.  Chair Review: Added text to clarify the structure of the
       document.

   h.  Chair Review: Added forward reference to the section covering
       BACKSLASH character encoding.

   i.  Removed the text that specifies when the sequence number MUST be
       incremented.  Text will be added to rfc2446bis.

   j.  Removed normative reference to RFC2822.

   k.  Changed reference of RFC4234 to RFC5234.

   l.  Few editorial changes.

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B.4.  Changes in -07

   A detailed list of changes is available at the following page:
   http://tools.ietf.org/wg/calsify/draft-ietf-calsify-rfc2445bis/
   draft-ietf-calsify-rfc2445bis-07.changes.html.

   a.  Issue 8: Clarified how to compute the exact duration of a nominal
       duration.

   b.  Issue 10: Added new examples for "VEVENT" and "VTODO" to
       demonstrate that end times are always non-inclusive, that is,
       even end times specified as DATE values.

   c.  Issue 11: Added a table that shows the dependency of BYxxx rule
       part expand or limit behaviour on the FREQ value in the rule.

   d.  Issue 19: Removed section "Registration of Content Type
       Elements".  Added registration templates in IANA Considerations
       section.  Specified how applications should treat x-name and
       x-token they don't recognize.

   e.  Issue 65: Removed 3rd recommended practice.  Added new
       requirements to require "DTEND" and "DUE" to be a local date time
       if and only if "DTSTART" is a local date time.

   f.  Issue 68: Clarified handling of date-times that fall in time
       discontinutities.

   g.  Issue 69: Clarified handling of recurrence instances that fall in
       time discontinutities

   h.  Issue 71: Clarified handling of leap seconds.

   i.  Issue 75: Clarified that the "RDATE" property MUST be specified
       as a local DATE-TIME value in "VTIMEZONE" sub-components.

   j.  Issue 76: Clarified that the value type of the "DTEND" property
       MUST be the same as the "DTSTART" property.

   k.  Issue 77: Clarified that the value type of the "DUE" property
       MUST be the same as the "DTSTART" property.

   l.  Issue 79: Clarified that "DTSTART" always specify an onset date-
       time of an observance and that its value does not need to be
       repeated in an "RDATE" property.

   m.  Issue 80: Rewrote Security Considerations section.

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   n.  Issue 81: Clarified the meaning of "the set of events specified
       by the rule" in the description of the BYSETPOS rule part.

   o.  Modified Abstract section.

   p.  Moved text of section 2.3 International Considerations at the end
       of sectino 2.1 Formatting Conventions.

   q.  Added Internationalization Considerations section.

   r.  Modified the description of the following properties: "ATTACH",
       "COMMENT", "COMPLETED", "CREATED" "DTSTAMP" "DUE", and "REPEAT".

   s.  Clarified some differences with ISO 8601.

   t.  Updated reference to CalDAV and ISO 8601.

   u.  Updated section "Differences from RFC 2445": added new
       restrictions and added list of removed restrictions.

   v.  Numerous editorial changes.

B.5.  Changes in -06

   A detailed list of changes is available at the following page:
   http://tools.ietf.org/wg/calsify/draft-ietf-calsify-rfc2445bis/
   draft-ietf-calsify-rfc2445bis-06.changes.html.

   a.  Issue 19: Defined new IANA registries.  [Work in progress];

   b.  Issue 23: Clarified that the UNTIL rule part MUST specify a value
       of the same type as the value specified by "DTSTART";

   c.  Issue 27: Clarified how the duration of generated recurrence
       instances is determined;

   d.  Issue 35: Further clarified the description of the "LANGUAGE"
       property;

   e.  Issue 42: Removed the restriction on the values allowed for the
       "ACTION" property in the the "VALARM" component;

   f.  Issue 47: Clarified that alarm triggers relative to a DATE value
       type needs to be triggered to 00:00:00 of the user's configured
       time zone;

   g.  Issue 56: Added a note to specify that FREQ MUST be specified as
       the first rule part in generated iCalendar applications, but MUST

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       be accepted in any order to ensure backward compatibility.  The
       rest of the RECUR value type ABNF has been further simplified;

   h.  Issue 59: Clarified the default duration of "VEVENT" components
       specified with a "DTSTART" property of DATE value type;

   i.  Issue 61: Modified all the property ABNFs to allow iana-param in
       addition to x-param.  Also modified the component ABNFs to allow
       iana-prop in addition to x-prop.  [Work in progress];

   j.  Issue 62: Removed the text that lead to believe that the
       "RECURRENCE-ID" of a specific recurrence instance might change;

   k.  Issue 64: Clarified that REQUEST-STATUS only allows pairs (1.1)
       and 3-tuples (1.1.1).

   l.  Issue 65: Clarified that a different time zone may be used by
       "DTSTART" and "DTEND", and "DTSTART" and "DUE" when specified as
       date with local time and time zone reference.  [Work in
       progress];

   m.  Issue 66: Clarified that if the "RDATE" property is specified as
       a PERIOD, its duration has precedence over the duration of the
       recurrence instance defined by the "DTSTART" property;

   n.  Issue 72: Removed the requirement that a "VTIMEZONE" calendar
       component MUST be present if the iCalendar object contains an
       RRULE that generates dates on both sides of a time zone shift;

   o.  Issue 73: Clarified that the "TZID" must be unique in the scope
       of an iCalendar object only;

   p.  Issue 74: Deprecated the "PROCEDURE" value for the "ACTION"
       property;

   q.  Issue 78: Fixed the text to specify that "TZOFFSETFROM" and not
       "TZOFFSETTO" must be used with "DTSTART" when generating the
       onset date-time values from the "RRULE" in a "VTIMEZONE"
       component;

   r.  Clarified that the "DTSTART" property MUST be specified in a
       "VTODO" component when the "DURATION" property is specified;

   s.  Started to update the time zone information / examples;

   t.  Numerous editorial changes.

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B.6.  Changes in -05

   A detailed list of changes is available at the following page:
   http://tools.ietf.org/wg/calsify/draft-ietf-calsify-rfc2445bis/
   draft-ietf-calsify-rfc2445bis-05.changes.html.

   a.  Fixed ABNF with references in .txt version of the draft;

   b.  Numerous editorial changes;

   c.  Clarified that normative statements in ABNF comments should be
       considered as normative;

   d.  Removed notes talking of character sets other than US-ASCII and
       UTF-8;

   e.  Renamed CTL to CONTROL to avoid conflict with the CTL rule
       defined in RFC4234;

   f.  Removed ABNF rules defined in RFC4234;

   g.  Changed the partstatparam ABNF rule for clarity;

   h.  Clarified the purpose of negative durations;

   i.  Added informational references to RFC 2392 (CID URL) and RFC 4516
       (LDAP URL).

   j.  Updated TZDB reference.

B.7.  Changes in -04

   A detailed list of changes is available at the following page:
   http://tools.ietf.org/wg/calsify/draft-ietf-calsify-rfc2445bis/
   draft-ietf-calsify-rfc2445bis-04.changes.html.

   a.  Issue 16: Clarified that recurrence instances, generated by a
       recurrence rule, with an invalid date or nonexistent local time
       must be ignored and not counted as part of the recurrence set.

   b.  Issue 26: Clarified how to handle the BYHOUR, BYMINUTE and
       BYSECOND rule parts when "DTSTART" is a DATE value.

   c.  Issue 28: Removed the MUST requirement to specify the "RDATE"
       property whenever the duration of a recurrence instance is
       modified.

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   d.  Issue 29: Clarified that the "DTSTART" property is REQUIRED in
       all types of recurring components.

   e.  Issue 32: Introduced the notion of an "iCalendar stream" to make
       it explicit when we are refering to a "single iCalendar object"
       or a "sequence of iCalendar objects".

   f.  Issue 34: Clarified what should be done with the "method"
       parameter when the iCalendar stream is a sequence of iCalendar
       objects.

   g.  Issue 40: Changed to fbprop ABNF rule to specify that the
       "DTSTAMP" and the "UID" properties are REQUIRED in "VFREEBUSY"
       components.

   h.  Issue 43: Removed the MUST requirement to specify the "DTSTART"
       and the "DTEND" properties as local time in recurring components,
       but added a note that in most cases this is the right thing to
       do.

   i.  Issue 44: Changed the x-prop ABNF to allow any parameters on non-
       standard properties.

   j.  Issue 46: Simplified the tzprop, audioprop, dispprop, emailprop,
       and procprop ABNF rules by removing the number of required
       properties in front of the "*".

   k.  Issue 48: Deprecated the "RANGE" parameter.

   l.  Issue 51: Clarified implicit duration of day events with no
       "DTEND" nor "DURATION" property.

   m.  Issue 52: Removed x-name from the "recur" rule part definition.
       It should be sufficient to allow xparam on properties of RECUR
       value type.

   n.  Issue 53: Updated the NON-US-ASCII ABNF rule for UTF-8.

   o.  Issue 56: Changed the "recur" ABNF rule to allow rule parts to be
       specified in any order.

   p.  Issue 57: Specified that the "DURATION" property MUST be
       specified as a "dur-day" or "dur-week" value when the "DTSTART"
       is a DATE.

   q.  Issue 58: Changed the jourprop ABNF rule to allow the
       "DESCRIPTION" property to occur more than once.

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   r.  Numerous editorial changes.

   s.  Changed reference to RFC 4646 for Language-Tag.

B.8.  Changes in -03

   A detailed list of changes is available at the following page:
   http://tools.ietf.org/wg/calsify/draft-ietf-calsify-rfc2445bis/
   draft-ietf-calsify-rfc2445bis-03.changes.html.

   a.  Numerous editorial changes.

   b.  Specified that "DTSTART" should match the pattern of "RRULE" and
       is always part of the "COUNT".

   c.  Specified "RRULE" should not occur more than once in recurring
       components.

   d.  Deprecated "EXRULE".

   e.  Fixed all ABNF errors reported by Bill Fenner's ABNF parsing web
       service available at:
       http://rtg.ietf.org/~fenner/abnf.cgi.

   f.  Changed reference to RFC 4648 for Base64 encoding.

B.9.  Changes in -02

   A detailed list of changes is available at the following page:
   http://tools.ietf.org/wg/calsify/draft-ietf-calsify-rfc2445bis/
   draft-ietf-calsify-rfc2445bis-02.changes.html.

   a.  Numerous editorial changes including the typos listed in the
       "RFC2445 Errata":
       http://www.rfc-editor.org/cgi-bin/errataSearch.pl?rfc=2445&
       and in the "RFC2445 Issues List":
       http://www.softwarestudio.org/iCal/2445Issues.html.

   b.  Clarified line folding requirements.

   c.  Clarified charset requirements.

   d.  Clarified line limits requirements.

   e.  Clarified on the use of the "LANGUAGE" parameter.

   f.  Fixed the eventprop, todoprop and jourprop ABNF rules with
       respect to required properties.

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   g.  Fixed all the examples to use RFC2606-compliant FQDNs.

   h.  Fixed the Content-ID URLs in the examples.

   i.  Fixed the LDAP URLs in the examples.

   j.  Moved multiple references in the Informative References section.

   k.  Updated the Acknowledgments section.

B.10.  Changes in -01

   A detailed list of changes is available at the following page:
   http://tools.ietf.org/wg/calsify/draft-ietf-calsify-rfc2445bis/
   draft-ietf-calsify-rfc2445bis-01.changes.html.

   a.  Numerous editorial changes (typos, errors in examples, etc.).

   b.  Fixed invalid media types in examples.

   c.  Fixed the "DTSTAMP" values in the examples.

   d.  Moved media type registration in a separate IANA Consideration
       section.

   e.  Added Internationalization Considerations section.

   f.  Added Security Considerations section.

   g.  Updated the Acknowledgments section.

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Author's Address

   Bernard Desruisseaux (editor)
   Oracle Corporation
   600 blvd. de Maisonneuve West
   Suite 1900
   Montreal, QC  H3A 3J2
   CANADA

   EMail: bernard.desruisseaux@oracle.com
   URI:   http://www.oracle.com/

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