JSCalendar: A JSON representation of calendar data
draft-ietf-calext-jscalendar-30

Versions: (draft-jenkins-jscalendar) 00 01 02 03         Standards Track
          04 05 06 07 08 09 10 11 12 13 14 15 16                        
          17 18 19 20 21 22 23 24 25 26 27 28 29                        
          30                                                            
Calendaring extensions                                        N. Jenkins
Internet-Draft                                               R. Stepanek
Intended status: Standards Track                                Fastmail
Expires: March 10, 2021                                September 6, 2020


           JSCalendar: A JSON representation of calendar data
                    draft-ietf-calext-jscalendar-30

Abstract

   This specification defines a data model and JSON representation of
   calendar data that can be used for storage and data exchange in a
   calendaring and scheduling environment.  It aims to be an alternative
   and, over time, successor to the widely deployed iCalendar data
   format, and to be unambiguous, extendable, and simple to process.  In
   contrast to the jCal format, which is also JSON-based, JSCalendar is
   not a direct mapping from iCalendar, but defines the data model
   independently and expands semantics where appropriate.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 10, 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Motivation and Relation to iCalendar and jCal . . . . . .   5
     1.2.  Notational Conventions  . . . . . . . . . . . . . . . . .   6
     1.3.  Type Signatures . . . . . . . . . . . . . . . . . . . . .   6
     1.4.  Data Types  . . . . . . . . . . . . . . . . . . . . . . .   7
       1.4.1.  Int . . . . . . . . . . . . . . . . . . . . . . . . .   7
       1.4.2.  UnsignedInt . . . . . . . . . . . . . . . . . . . . .   7
       1.4.3.  UTCDateTime . . . . . . . . . . . . . . . . . . . . .   7
       1.4.4.  LocalDateTime . . . . . . . . . . . . . . . . . . . .   7
       1.4.5.  Duration  . . . . . . . . . . . . . . . . . . . . . .   8
       1.4.6.  SignedDuration  . . . . . . . . . . . . . . . . . . .   9
       1.4.7.  Id  . . . . . . . . . . . . . . . . . . . . . . . . .  10
       1.4.8.  PatchObject . . . . . . . . . . . . . . . . . . . . .  10
       1.4.9.  Time Zones  . . . . . . . . . . . . . . . . . . . . .  11
       1.4.10. Relation  . . . . . . . . . . . . . . . . . . . . . .  11
   2.  JSCalendar Objects  . . . . . . . . . . . . . . . . . . . . .  12
     2.1.  JSEvent . . . . . . . . . . . . . . . . . . . . . . . . .  12
     2.2.  JSTask  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     2.3.  JSGroup . . . . . . . . . . . . . . . . . . . . . . . . .  12
   3.  Structure of JSCalendar Objects . . . . . . . . . . . . . . .  13
     3.1.  Object Type . . . . . . . . . . . . . . . . . . . . . . .  13
     3.2.  Normalization and Equivalence . . . . . . . . . . . . . .  13
     3.3.  Vendor-specific Property Extensions, Values and Types . .  13
   4.  Common JSCalendar Properties  . . . . . . . . . . . . . . . .  14
     4.1.  Metadata Properties . . . . . . . . . . . . . . . . . . .  14
       4.1.1.  @type . . . . . . . . . . . . . . . . . . . . . . . .  14
       4.1.2.  uid . . . . . . . . . . . . . . . . . . . . . . . . .  14
       4.1.3.  relatedTo . . . . . . . . . . . . . . . . . . . . . .  15
       4.1.4.  prodId  . . . . . . . . . . . . . . . . . . . . . . .  15
       4.1.5.  created . . . . . . . . . . . . . . . . . . . . . . .  15
       4.1.6.  updated . . . . . . . . . . . . . . . . . . . . . . .  16
       4.1.7.  sequence  . . . . . . . . . . . . . . . . . . . . . .  16
       4.1.8.  method  . . . . . . . . . . . . . . . . . . . . . . .  16
     4.2.  What and Where Properties . . . . . . . . . . . . . . . .  16
       4.2.1.  title . . . . . . . . . . . . . . . . . . . . . . . .  16
       4.2.2.  description . . . . . . . . . . . . . . . . . . . . .  16
       4.2.3.  descriptionContentType  . . . . . . . . . . . . . . .  16
       4.2.4.  showWithoutTime . . . . . . . . . . . . . . . . . . .  17
       4.2.5.  locations . . . . . . . . . . . . . . . . . . . . . .  17
       4.2.6.  virtualLocations  . . . . . . . . . . . . . . . . . .  18
       4.2.7.  links . . . . . . . . . . . . . . . . . . . . . . . .  19
       4.2.8.  locale  . . . . . . . . . . . . . . . . . . . . . . .  21



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       4.2.9.  keywords  . . . . . . . . . . . . . . . . . . . . . .  21
       4.2.10. categories  . . . . . . . . . . . . . . . . . . . . .  21
       4.2.11. color . . . . . . . . . . . . . . . . . . . . . . . .  21
     4.3.  Recurrence Properties . . . . . . . . . . . . . . . . . .  22
       4.3.1.  recurrenceId  . . . . . . . . . . . . . . . . . . . .  22
       4.3.2.  recurrenceRules . . . . . . . . . . . . . . . . . . .  22
       4.3.3.  excludedRecurrenceRules . . . . . . . . . . . . . . .  31
       4.3.4.  recurrenceOverrides . . . . . . . . . . . . . . . . .  31
       4.3.5.  excluded  . . . . . . . . . . . . . . . . . . . . . .  32
     4.4.  Sharing and Scheduling Properties . . . . . . . . . . . .  32
       4.4.1.  priority  . . . . . . . . . . . . . . . . . . . . . .  32
       4.4.2.  freeBusyStatus  . . . . . . . . . . . . . . . . . . .  33
       4.4.3.  privacy . . . . . . . . . . . . . . . . . . . . . . .  33
       4.4.4.  replyTo . . . . . . . . . . . . . . . . . . . . . . .  34
       4.4.5.  participants  . . . . . . . . . . . . . . . . . . . .  35
     4.5.  Alerts Properties . . . . . . . . . . . . . . . . . . . .  40
       4.5.1.  useDefaultAlerts  . . . . . . . . . . . . . . . . . .  40
       4.5.2.  alerts  . . . . . . . . . . . . . . . . . . . . . . .  40
     4.6.  Multilingual Properties . . . . . . . . . . . . . . . . .  43
       4.6.1.  localizations . . . . . . . . . . . . . . . . . . . .  43
     4.7.  Time Zone Properties  . . . . . . . . . . . . . . . . . .  43
       4.7.1.  timeZone  . . . . . . . . . . . . . . . . . . . . . .  43
       4.7.2.  timeZones . . . . . . . . . . . . . . . . . . . . . .  44
   5.  Type-specific JSCalendar Properties . . . . . . . . . . . . .  46
     5.1.  JSEvent Properties  . . . . . . . . . . . . . . . . . . .  46
       5.1.1.  start . . . . . . . . . . . . . . . . . . . . . . . .  46
       5.1.2.  duration  . . . . . . . . . . . . . . . . . . . . . .  46
       5.1.3.  status  . . . . . . . . . . . . . . . . . . . . . . .  46
     5.2.  JSTask Properties . . . . . . . . . . . . . . . . . . . .  47
       5.2.1.  due . . . . . . . . . . . . . . . . . . . . . . . . .  47
       5.2.2.  start . . . . . . . . . . . . . . . . . . . . . . . .  47
       5.2.3.  estimatedDuration . . . . . . . . . . . . . . . . . .  47
       5.2.4.  percentComplete . . . . . . . . . . . . . . . . . . .  47
       5.2.5.  progress  . . . . . . . . . . . . . . . . . . . . . .  47
       5.2.6.  progressUpdated . . . . . . . . . . . . . . . . . . .  48
     5.3.  JSGroup Properties  . . . . . . . . . . . . . . . . . . .  48
       5.3.1.  entries . . . . . . . . . . . . . . . . . . . . . . .  49
       5.3.2.  source  . . . . . . . . . . . . . . . . . . . . . . .  49
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  49
     6.1.  Simple event  . . . . . . . . . . . . . . . . . . . . . .  50
     6.2.  Simple task . . . . . . . . . . . . . . . . . . . . . . .  50
     6.3.  Simple group  . . . . . . . . . . . . . . . . . . . . . .  50
     6.4.  All-day event . . . . . . . . . . . . . . . . . . . . . .  51
     6.5.  Task with a due date  . . . . . . . . . . . . . . . . . .  51
     6.6.  Event with end time zone  . . . . . . . . . . . . . . . .  52
     6.7.  Floating-time event (with recurrence) . . . . . . . . . .  52
     6.8.  Event with multiple locations and localization  . . . . .  53
     6.9.  Recurring event with overrides  . . . . . . . . . . . . .  54



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     6.10. Recurring event with participants . . . . . . . . . . . .  55
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  57
     7.1.  Expanding Recurrences . . . . . . . . . . . . . . . . . .  57
     7.2.  JSON Parsing  . . . . . . . . . . . . . . . . . . . . . .  57
     7.3.  URI Values  . . . . . . . . . . . . . . . . . . . . . . .  58
     7.4.  Spam  . . . . . . . . . . . . . . . . . . . . . . . . . .  58
     7.5.  Duplication . . . . . . . . . . . . . . . . . . . . . . .  59
     7.6.  Time Zones  . . . . . . . . . . . . . . . . . . . . . . .  59
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  59
     8.1.  Media Type Registration . . . . . . . . . . . . . . . . .  59
     8.2.  Creation of "JSCalendar Properties" Registry  . . . . . .  60
       8.2.1.  Preliminary Community Review  . . . . . . . . . . . .  61
       8.2.2.  Submit Request to IANA  . . . . . . . . . . . . . . .  61
       8.2.3.  Designated Expert Review  . . . . . . . . . . . . . .  61
       8.2.4.  Change Procedures . . . . . . . . . . . . . . . . . .  62
       8.2.5.  JSCalendar Properties Registry Template . . . . . . .  62
       8.2.6.  Initial Contents for the JSCalendar Properties
               Registry  . . . . . . . . . . . . . . . . . . . . . .  63
     8.3.  Creation of "JSCalendar Types" Registry . . . . . . . . .  71
       8.3.1.  JSCalendar Types Registry Template  . . . . . . . . .  71
       8.3.2.  Initial Contents for the JSCalendar Types Registry  .  71
     8.4.  Creation of "JSCalendar Enum Values" Registry . . . . . .  73
       8.4.1.  JSCalendar Enum Property Template . . . . . . . . . .  73
       8.4.2.  JSCalendar Enum Value Template  . . . . . . . . . . .  73
       8.4.3.  Initial Contents for the JSCalendar Enum Registry . .  73
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  79
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  79
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  79
     10.2.  Informative References . . . . . . . . . . . . . . . . .  81
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  82

1.  Introduction

   This document defines a data model for calendar event and task
   objects, or groups of such objects, in electronic calendar
   applications and systems.  The format aims to be unambiguous,
   extendable and simple to process.

   The key design considerations for this data model are as follows:

   o  The attributes of the calendar entry represented must be described
      as simple key-value pairs.  Simple events are simple to represent;
      complex events can be modelled accurately.

   o  Wherever possible, there should be only one way to express the
      desired semantics, reducing complexity.





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   o  The data model should avoid ambiguities, which often lead to
      interoperability issues between implementations.

   o  The data model should be compatible with the iCalendar data format
      [RFC5545] [RFC7986] and extensions, but the specification should
      add new attributes where the iCalendar format currently lacks
      expressivity, and drop seldom-used, obsolete, or redundant
      properties.  This means translation with no loss of semantics
      should be easy with most common iCalendar files.

   o  Extensions, such as new properties and components, should not
      require updates to this document.

   The representation of this data model is defined in the I-JSON format
   [RFC7493], which is a strict subset of the JavaScript Object Notation
   (JSON) Data Interchange Format [RFC8259].  Using JSON is mostly a
   pragmatic choice: its widespread use makes JSCalendar easier to
   adopt, and the ready availability of production-ready JSON
   implementations eliminates a whole category of parser-related
   interoperability issues, which iCalendar has often suffered from.

1.1.  Motivation and Relation to iCalendar and jCal

   The iCalendar data format [RFC5545], a widely deployed interchange
   format for calendaring and scheduling data, has served calendaring
   vendors for a long while, but contains some ambiguities and pitfalls
   that can not be overcome without backward-incompatible changes.

   Sources of implementation errors include the following:

   o  iCalendar defines various formats for local times, UTC time, and
      dates.

   o  iCalendar requires custom time zone definitions within a single
      calendar component.

   o  iCalendar's definition of recurrence rules is ambiguous and has
      resulted in differing understandings even between experienced
      calendar developers.

   o  The iCalendar format itself causes interoperability issues due to
      misuse of CRLF-terminated strings, line continuations, and subtle
      differences among iCalendar parsers.

   In recent years, many new products and services have appeared that
   wish to use a JSON representation of calendar data within their APIs.
   The JSON format for iCalendar data, jCal [RFC7265], is a direct
   mapping between iCalendar and JSON.  In its effort to represent full



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   iCalendar semantics, it inherits all the same pitfalls and uses a
   complicated JSON structure.

   As a consequence, since the standardization of jCal, the majority of
   implementations and service providers either kept using iCalendar, or
   came up with their own proprietary JSON representations, which are
   incompatible with each other and often suffer from common pitfalls,
   such as storing event start times in UTC (which become incorrect if
   the timezone's rules change in the future).  JSCalendar meets the
   demand for JSON-formatted calendar data that is free of such known
   problems and provides a standard representation as an alternative to
   the proprietary formats.

1.2.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The underlying format used for this specification is JSON.
   Consequently, the terms "object" and "array" as well as the four
   primitive types (strings, numbers, booleans, and null) are to be
   interpreted as described in Section 1 of [RFC8259].

   Some examples in this document contain "partial" JSON documents used
   for illustrative purposes.  In these examples, three periods "..."
   are used to indicate a portion of the document that has been removed
   for compactness.

1.3.  Type Signatures

   Type signatures are given for all JSON values in this document.  The
   following conventions are used:

   o  "*" - The type is undefined (the value could be any type, although
      permitted values may be constrained by the context of this value).

   o  "String" - The JSON string type.

   o  "Number" - The JSON number type.

   o  "Boolean" - The JSON boolean type.

   o  "A[B]" - A JSON object where the keys are all of type "A", and the
      values are all of type "B".




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   o  "A[]" - An array of values of type "A".

   o  "A|B" - The value is either of type "A" or of type "B".

   Other types may also be given, with their representations defined
   elsewhere in this document.

1.4.  Data Types

   In addition to the standard JSON data types, the following data types
   are used in this specification:

1.4.1.  Int

   Where "Int" is given as a data type, it means an integer in the range
   -2^53+1 <= value <= 2^53-1, the safe range for integers stored in a
   floating-point double, represented as a JSON "Number".

1.4.2.  UnsignedInt

   Where "UnsignedInt" is given as a data type, it means an integer in
   the range 0 <= value <= 2^53-1, represented as a JSON "Number".

1.4.3.  UTCDateTime

   This is a string in [RFC3339] "date-time" format, with the further
   restrictions that any letters MUST be in uppercase, the time
   component MUST be included and the time offset MUST be the character
   "Z".  Fractional second values MUST NOT be included unless non-zero
   and MUST NOT have trailing zeros, to ensure there is only a single
   representation for each date-time.

   For example "2010-10-10T10:10:10.003Z" is OK, but
   "2010-10-10T10:10:10.000Z" is invalid and is correctly encoded as
   "2010-10-10T10:10:10Z".

1.4.4.  LocalDateTime

   This is a date-time string with no time zone/offset information.  It
   is otherwise in the same format as UTCDateTime, including fractional
   seconds.  For example "2006-01-02T15:04:05" and
   "2006-01-02T15:04:05.003" are both valid.  The time zone to associate
   the LocalDateTime with comes from an associated property, or if no
   time zone is associated it defines "floating time".  Floating date-
   times are not tied to any specific time zone.  Instead, they occur in
   each time zone at the given wall-clock time (as opposed to the same
   instant point in time).




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   A time zone may have a period of discontinuity, for example a change
   from standard time to daylight-savings time.  When converting local
   date-times that fall in the discontinuity to UTC, the offset before
   the transition is used.

   For example, in the America/Los_Angeles time zone, the date-time
   2020-11-01T01:30:00 occurs twice: before the DST transition with a
   UTC offset of -07:00, and again after the transition with an offset
   of -08:00.  When converting to UTC, we therefore use the offset
   before the transition (-07:00) and so it becomes
   2020-11-01T08:30:00Z.

   Similarly, in the Australia/Melbourne time zone, the date-time
   2020-10-04T02:30:00 does not exist: the clocks are moved forward one
   hour for DST on that day at 02:00.  However, such a value may appear
   during calculations (see duration semantics below), or due to a
   change in time zone rules (so it was valid when the event was first
   created).  Again, it is interpreted as though the offset before the
   transition is in effect (+10:00), therefore when converted to UTC we
   get 2020-10-03T16:30:00Z.

1.4.5.  Duration

   Where Duration is given as a type, it means a length of time
   represented by a subset of ISO8601 duration format, as specified by
   the following ABNF [RFC5234]:

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

       duration    = "P" (dur-cal [dur-time] / dur-cal / dur-time)

   In addition, the duration MUST NOT include fractional second values
   unless the fraction is non-zero.

   A duration specifies an abstract number of weeks, days, hours,
   minutes, and/or seconds.  A duration specified using weeks or days
   does not always correspond to an exact multiple of 24 hours.  The
   number of hours/minutes/seconds may vary if it overlaps a period of
   discontinuity in the event's time zone, for example a change from
   standard time to daylight-savings time.  Leap seconds MUST NOT be




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   considered when adding or subtracting a duration to/from a
   LocalDateTime.

   To add a duration to a LocalDateTime:

   1.  Add any week or day components of the duration to the date.

   2.  If a time zone applies to the LocalDateTime, convert it to a
       UTCDateTime following the semantics in Section 1.4.4.

   3.  Add any hour, minute or second components of the duration (in
       absolute time).

   4.  Convert the resulting UTCDateTime back to a LocalDateTime in the
       time zone that applies.

   To subtract a duration from a LocalDateTime, the steps apply in
   reverse:

   1.  If a time zone applies to the LocalDateTime, convert it to UTC
       following the semantics in Section 1.4.4.

   2.  Subtract any hour, minute or second components of the duration
       (in absolute time).

   3.  Convert the resulting UTCDateTime back to LocalDateTime in the
       time zone that applies.

   4.  Subtract any week or day components of the duration from the
       date.

   5.  If the resulting time does not exist on the date due to a
       discontinuity in the time zone, use the semantics in
       Section 1.4.4 to convert to UTC and back to get a valid
       LocalDateTime.

   These semantics match the iCalendar DURATION value type ([RFC5545],
   Section 3.3.6).

1.4.6.  SignedDuration

   A SignedDuration represents a length of time that may be positive or
   negative and is typically used to express the offset of a point in
   time relative to an associated time.  It is represented as a
   Duration, optionally preceded by a sign character.  It is specified
   by the following ABNF:

       signed-duration = ["+" / "-"] duration



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   A negative sign indicates a point in time at or before the associated
   time, a positive or no sign a time at or after the associated time.

1.4.7.  Id

   Where "Id" is given as a data type, it means a "String" of at least 1
   and a maximum of 255 octets in size, and it MUST only contain
   characters from the "URL and Filename Safe" base64url alphabet, as
   defined in Section 5 of [RFC4648], excluding the pad character ("=").
   This means the allowed characters are the ASCII alphanumeric
   characters ("A-Za-z0-9"), hyphen ("-"), and underscore ("_").

   Unless otherwise specified, Ids are arbitrary and only have meaning
   within the object where they are being used.  Ids need not be unique
   among different objects.  For example, two JSEvent objects might use
   the same ids in their respective "links" properties.  Or within the
   same JSEvent object the same Id could appear in the "participants"
   and "alerts" properties.  These situations do not imply any semantic
   connections among the objects.

   Nevertheless, a UUID is typically a good choice.

1.4.8.  PatchObject

   A PatchObject is of type "String[*]", and represents an unordered set
   of patches on a JSON object.  Each key is a path represented in a
   subset of JSON pointer format [RFC6901].  The paths have an implicit
   leading "/", so each key is prefixed with "/" before applying the
   JSON pointer evaluation algorithm.

   A patch within a PatchObject is only valid if all of the following
   conditions apply:

   1.  The pointer MUST NOT insert/delete from an array; the array MUST
       be replaced in its entirety instead.

   2.  When evaluating a path, all parts prior to the last (i.e., the
       value after the final slash) MUST exist.

   3.  There MUST NOT be two patches in the PatchObject where the
       pointer of one is a prefix of the pointer of the other, e.g.,
       "alerts/foo/offset" and "alerts".

   4.  The value for the patch MUST be valid for the property being set
       (of the correct type and obeying any other applicable
       restrictions), or if null the property MUST be optional.

   The value associated with each pointer is either:



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   o  null: Remove the property at the given path from the patched
      object.  If the property is not present in the object, this a no-
      op.

   o  Anything else: Set the value for the property to this value (this
      may be a replacement or addition to the object being patched).

   A PatchObject does not define its own "@type" property.  A "@type"
   property in a patch MUST be handled as any other patched property
   value.

   Implementations MUST reject in its entirety a PatchObject if any of
   its patches is invalid.  Implementations MUST NOT apply partial
   patches.

1.4.9.  Time Zones

   By default, time zones in JSCalendar are identified by their names in
   the IANA Time Zone Database [TZDB], and the zone rules of the
   respective zone records apply.

   Implementations MAY embed the definitions of custom time zones in the
   "timeZones" property (see Section 4.7.2).

1.4.10.  Relation

   A Relation object defines the relation to other objects, using a
   possibly empty set of relation types.  The object that defines this
   relation is the linking object, while the other object is the linked
   object.  The Relation object has the following properties:

   o  @type: "String" (mandatory)

      Specifies the type of this object.  This MUST be "Relation".

   o  relation: "String[Boolean]" (optional, default: empty Object)

      Describes how the linked object is related to the linking object.
      The relation is defined as a set of relation types.  If empty, the
      relationship between the two objects is unspecified.

      Keys in the set MUST be one of the following values, or specified
      in the property definition where the Relation object is used, or a
      value registered in the IANA JSCalendar Enum Registry, or a
      vendor-specific value:

      *  "first": The linked object is the first in a series the linking
         object is part of.



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      *  "next": The linked object is the next in a series the linking
         object is part of.

      *  "child": The linked object is a subpart of the linking object.

      *  "parent": The linking object is a subpart of the linked object.

      The value for each key in the set MUST be true.

2.  JSCalendar Objects

   This section describes the calendar object types specified by
   JSCalendar.

2.1.  JSEvent

   Media type: "application/jscalendar+json;type=jsevent"

   A JSEvent represents a scheduled amount of time on a calendar,
   typically a meeting, appointment, reminder or anniversary.  It is
   required to start at a certain point in time and typically has a non-
   zero duration.  Multiple participants may partake in the event at
   multiple locations.

   The @type (Section 4.1.1) property value MUST be "jsevent".

2.2.  JSTask

   Media type: "application/jscalendar+json;type=jstask"

   A JSTask represents an action-item, assignment, to-do or work item.
   It may start and be due at certain points in time, may take some
   estimated time to complete, and may recur, none of which is required.

   The @type (Section 4.1.1) property value MUST be "jstask".

2.3.  JSGroup

   Media type: "application/jscalendar+json;type=jsgroup"

   A JSGroup is a collection of JSEvent (Section 2.1) and/or JSTask
   (Section 2.2) objects.  Typically, objects are grouped by topic
   (e.g., by keywords) or calendar membership.

   The @type (Section 4.1.1) property value MUST be "jsgroup".






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3.  Structure of JSCalendar Objects

   A JSCalendar object is a JSON object, which MUST be valid I-JSON (a
   stricter subset of JSON), as specified in [RFC8259].  Property names
   and values are case-sensitive.

   The object has a collection of properties, as specified in the
   following sections.  Properties are specified as being either
   mandatory or optional.  Optional properties may have a default value,
   if explicitly specified in the property definition.

3.1.  Object Type

   JSCalendar objects MUST name their type in the "@type" property, if
   not explicitly specified otherwise for the respective object type.  A
   notable exception to this rule is the PatchObject (Section 1.4.8).

3.2.  Normalization and Equivalence

   JSCalendar aims to provide unambiguous definitions for value types
   and properties, but does not define a general normalization or
   equivalence method for JSCalendar objects and types.  This is because
   the notion of equivalence might range from byte-level equivalence to
   semantic equivalence, depending on the respective use case.

   Normalization of JSCalendar objects is hindered because of the
   following reasons:

   o  Custom JSCalendar properties may contain arbitrary JSON values,
      including arrays.  However, equivalence of arrays might or might
      not depend on the order of elements, depending on the respective
      property definition.

   o  Several JSCalendar property values are defined as URIs and media
      types, but normalization of these types is inherently protocol-
      and scheme-specific, depending on the use-case of the equivalence
      definition (see Section 6 of [RFC3986]).

   Considering this, the definition of equivalence and normalization is
   left to client and server implementations and to be negotiated by a
   calendar exchange protocol or defined elsewhere.

3.3.  Vendor-specific Property Extensions, Values and Types

   Vendors MAY add additional properties to the calendar object to
   support their custom features.  To avoid conflict, the names of these
   properties MUST be prefixed by a domain name controlled by the vendor
   followed by a colon, e.g., "example.com:customprop".  If the value is



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   a new JSCalendar object, it either MUST include a "@type" property or
   it MUST explicitly be specified to not require a type designator.
   The type name MUST be prefixed with a domain name controlled by the
   vendor.

   Some JSCalendar properties allow vendor-specific value extensions.
   Such vendor-specific values MUST be prefixed by a domain name
   controlled by the vendor followed by a colon, e.g.,
   "example.com:customrel".

   Vendors are strongly encouraged to register any new property values
   or extensions that are useful to other systems as well, rather than
   use a vendor-specific prefix.

4.  Common JSCalendar Properties

   This section describes the properties that are common to the various
   JSCalendar object types.  Specific JSCalendar object types may only
   support a subset of these properties.  The object type definitions in
   Section 5 describe the set of supported properties per type.

4.1.  Metadata Properties

4.1.1.  @type

   Type: "String" (mandatory).

   Specifies the type which this object represents.  This MUST be one of
   the following values:

   o  "jsevent": a JSCalendar event (Section 2.1).

   o  "jstask": a JSCalendar task (Section 2.2).

   o  "jsgroup": a JSCalendar group (Section 2.3).

4.1.2.  uid

   Type: "String" (mandatory).

   A globally unique identifier, used to associate the object as the
   same across different systems, calendars and views.  The value of
   this property MUST be unique across all JSCalendar objects, even if
   they are of different type.  [RFC4122] describes a range of
   established algorithms to generate universally unique identifiers
   (UUID).  UUID version 4, described in Section 4.4 of [RFC4122], is
   RECOMMENDED.




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   For compatibility with [RFC5545] UIDs, implementations MUST be able
   to receive and persist values of at least 255 octets for this
   property, but they MUST NOT truncate values in the middle of a UTF-8
   multi-octet sequence.

4.1.3.  relatedTo

   Type: "String[Relation]" (optional).

   Relates the object to other JSCalendar objects.  This is represented
   as a map of the UIDs of the related objects to information about the
   relation.

   If an object is split to make a "this and future" change to a
   recurrence, the original object MUST be truncated to end at the
   previous occurrence before this split, and a new object created to
   represent all the occurrences after the split.  A "next" relation
   MUST be set on the original object's relatedTo property for the UID
   of the new object.  A "first" relation for the UID of the first
   object in the series MUST be set on the new object.  Clients can then
   follow these UIDs to get the complete set of objects if the user
   wishes to modify them all at once.

4.1.4.  prodId

   Type: "String" (optional).

   The identifier for the product that last updated the JSCalendar
   object.  This should be set whenever the data in the object is
   modified (i.e., whenever the "updated" property is set).

   The vendor of the implementation SHOULD ensure that this is a
   globally unique identifier, using some technique such as an FPI
   value, as defined in [ISO.9070.1991].  It MUST only use characters of
   an iCalendar TEXT data value (see Section 3.3.11 of [RFC5545]).

   This property SHOULD NOT be used to alter the interpretation of a
   JSCalendar object beyond the semantics specified in this document.
   For example, it is not to be used to further the understanding of
   non-standard properties, a practice that is knows to cause long-term
   interoperability problems.

4.1.5.  created

   Type: "UTCDateTime" (optional).

   The date and time this object was initially created.




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4.1.6.  updated

   Type: "UTCDateTime" (mandatory).

   The date and time the data in this object was last modified (or its
   creation date/time if not modified since).

4.1.7.  sequence

   Type: "UnsignedInt" (optional, default: 0).

   Initially zero, this MUST be incremented by one every time a change
   is made to the object, except if the change only modifies the
   "participants" property (see Section 4.4.5).

   This is used as part of iTIP [RFC5546] to know which version of the
   object a scheduling message relates to.

4.1.8.  method

   Type: "String" (optional).

   The iTIP [RFC5546] method, in lowercase.  This MUST only be present
   if the JSCalendar object represents an iTIP scheduling message.

4.2.  What and Where Properties

4.2.1.  title

   Type: "String" (optional, default: empty String).

   A short summary of the object.

4.2.2.  description

   Type: "String" (optional, default: empty String).

   A longer-form text description of the object.  The content is
   formatted according to the "descriptionContentType" property.

4.2.3.  descriptionContentType

   Type: "String" (optional, default: "text/plain").

   Describes the media type [RFC6838] of the contents of the
   "description" property.  Media types MUST be sub-types of type
   "text", and SHOULD be "text/plain" or "text/html" [MIME].  They MAY
   include parameters and the "charset" parameter value MUST be "utf-8",



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   if specified.  Descriptions of type "text/html" MAY contain "cid"
   URLs [RFC2392] to reference links in the calendar object by use of
   the "cid" property of the Link object.

4.2.4.  showWithoutTime

   Type: "Boolean" (optional, default: false).

   Indicates that the time is not important to display to the user when
   rendering this calendar object.  An example of this is an event that
   conceptually occurs all day or across multiple days, such as "New
   Year's Day" or "Italy Vacation".  While the time component is
   important for free-busy calculations and checking for scheduling
   clashes, calendars may choose to omit displaying it and/or display
   the object separately to other objects to enhance the user's view of
   their schedule.

   Such events are also commonly known as "all-day" events.

4.2.5.  locations

   Type: "Id[Location]" (optional).

   A map of location ids to Location objects, representing locations
   associated with the object.

   A Location object has the following properties.  It MUST have at
   least one property other than the "relativeTo" property.

   o  @type: "String" (mandatory)

      Specifies the type of this object.  This MUST be "Location".

   o  name: "String" (optional)

      The human-readable name of the location.

   o  description: "String" (optional)

      Human-readable, plain-text instructions for accessing this
      location.  This may be an address, set of directions, door access
      code, etc.

   o  locationTypes: "String[Boolean]" (optional)

      A set of one or more location types that describe this location.
      All types MUST be from the Location Types Registry [LOCATIONTYPES]
      as defined in [RFC4589].  The set is represented as a map, with



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      the keys being the location types.  The value for each key in the
      map MUST be true.

   o  relativeTo: "String" (optional)

      Specifies the relation between this location and the time of the
      JSCalendar object.  This is primarily to allow events representing
      travel to specify the location of departure (at the start of the
      event) and location of arrival (at the end); this is particularly
      important if these locations are in different time zones, as a
      client may wish to highlight this information for the user.

      This MUST be one of the following values, a value registered in
      the IANA JSCalendar Enum Registry, or a vendor-specific value.
      Any value the client or server doesn't understand should be
      treated the same as if this property is omitted.

      *  "start": The event/task described by this JSCalendar object
         occurs at this location at the time the event/task starts.

      *  "end": The event/task described by this JSCalendar object
         occurs at this location at the time the event/task ends.

   o  timeZone: "String" (optional)

      A time zone for this location.  See also Section 1.4.9.

   o  coordinates: "String" (optional)

      A "geo:" URI [RFC5870] for the location.

   o  linkIds: "Id[Boolean]" (optional)

      A set of link ids for links to alternative representations of this
      location.  Each key in the set MUST be the id of a Link object
      defined in the "links" property of this calendar object.  The
      value for each key in the set MUST be true.  If there are no
      links, this MUST be omitted (rather than specified as an empty
      set).

      For example, an alternative representation could be in vCard
      format.

4.2.6.  virtualLocations

   Type: "Id[VirtualLocation]" (optional).





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   A map of ids to VirtualLocation objects, representing virtual
   locations, such as video conferences or chat rooms, associated with
   the object.

   A VirtualLocation object has the following properties.

   o  @type: "String" (mandatory)

      Specifies the type of this object.  This MUST be
      "VirtualLocation".

   o  name: "String" (optional, default: empty String)

      The human-readable name of the virtual location.

   o  description: "String" (optional)

      Human-readable plain-text instructions for accessing this
      location.  This may be an address, set of directions, door access
      code, etc.

   o  uri: "String" (mandatory)

      A URI that represents how to connect to this virtual location.

      This may be a telephone number (represented using the "tel:"
      scheme, e.g., "tel:+1-555-555-555") for a teleconference, a web
      address for online chat, or any custom URI.

4.2.7.  links

   Type: "Id[Link]" (optional).

   A map of link ids to Link objects, representing external resources
   associated with the object.

   A Link object has the following properties:

   o  @type: "String" (mandatory)

      Specifies the type of this object.  This MUST be "Link".

   o  href: "String" (mandatory)

      A URI from which the resource may be fetched.






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      This MAY be a "data:" URL [RFC2397], but it is recommended that
      the file be hosted on a server to avoid embedding arbitrarily
      large data in JSCalendar object instances.

   o  cid: "String" (optional)

      This MUST be a valid "content-id" value according to the
      definition of Section 2 in [RFC2392].  The value MUST be unique
      within this Link object but has no meaning beyond that.  It MAY be
      different from the link id for this Link object.

   o  contentType: "String" (optional)

      The media type [RFC6838] of the resource, if known.

   o  size: "UnsignedInt" (optional)

      The size, in octets, of the resource when fully decoded (i.e., the
      number of octets in the file the user would download), if known.
      Note that this is an informational estimate, and implementations
      must be prepared to handle the actual size being quite different
      when the resource is fetched.

   o  rel: "String" (optional)

      Identifies the relation of the linked resource to the object.  If
      set, the value MUST be a relation type from the IANA registry
      [LINKRELS], as established in [RFC8288].

      Links with a rel of "enclosure" MUST be considered by the client
      as attachments for download.

      Links with a rel of "describedby" MUST be considered by the client
      to be an alternative representation of the description.

      Links with a rel of "icon" MUST be considered by the client to be
      an image that it may use when presenting the calendar data to a
      user.  The "display" property may be set to indicate the purpose
      of this image.

   o  display: "String" (optional)

      Describes the intended purpose of a link to an image.  If set, the
      "rel" property MUST be set to "icon".  The value MUST be one of
      the following values, a value registered in the IANA JSCalendar
      Enum Registry, or a vendor-specific value:





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      *  "badge": an image meant to be displayed alongside the title of
         the object.

      *  "graphic": a full image replacement for the object itself.

      *  "fullsize": an image that is used to enhance the object.

      *  "thumbnail": a smaller variant of "fullsize" to be used when
         space for the image is constrained.

   o  title: "String" (optional)

      A human-readable plain-text description of the resource.

4.2.8.  locale

   Type: "String" (optional).

   The language tag as defined in [RFC5646] that best describes the
   locale used for the text in the calendar object, if known.

4.2.9.  keywords

   Type: "String[Boolean]" (optional).

   A set of keywords or tags that relate to the object.  The set is
   represented as a map, with the keys being the keywords.  The value
   for each key in the map MUST be true.

4.2.10.  categories

   Type: "String[Boolean]" (optional).

   A set of categories that relate to the calendar object.  The set is
   represented as a map, with the keys being the categories specified as
   URIs.  The value for each key in the map MUST be true.

   In contrast to keywords, categories typically are structured.  For
   example, a vendor owning the domain "example.com" might define the
   categories "http://example.com/categories/sports/american-football"
   and "http://example.com/categories/music/r-b".

4.2.11.  color

   Type: "String" (optional).

   A color clients MAY use when displaying this calendar object.  The
   value is a color name taken from the set of names defined in



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   Section 4.3 of CSS Color Module Level 3 [COLORS], or an RGB value in
   hexadecimal notation, as defined in Section 4.2.1 of CSS Color Module
   Level 3.

4.3.  Recurrence Properties

   Some events and tasks occur at regular or irregular intervals.
   Rather than having to copy the data for every occurrence there can be
   a master event with rules to generate recurrences, and/or overrides
   that add extra dates or exceptions to the rules.

   The recurrence set is the compelete set of instances for an object.
   It is generated by considering the following properties in order, all
   of which are optional:

   1.  The recurrenceRules property (Section 4.3.2) generates a set of
       extra date-times on which the object occurs.

   2.  The excludedRecurrenceRules property (Section 4.3.3) generates a
       set of date-times that are to be removed from the previously
       generated set of date-times on which the object occurs.

   3.  The recurrenceOverrides property (Section 4.3.4) defines date-
       times which are added or excluded to form the final set.  (This
       property may also contain changes to the object to apply to
       particular instances.)

4.3.1.  recurrenceId

   Type: "LocalDateTime" (optional).

   If present, this JSCalendar object represents one occurrence of a
   recurring JSCalendar object.  If present the "recurrenceRules" and
   "recurrenceOverrides" properties MUST NOT be present.

   The value is a date-time either produced by the "recurrenceRules" of
   the master event, or added as a key to the "recurrenceOverrides"
   property of the master event.

4.3.2.  recurrenceRules

   Type: "RecurrenceRule[]" (optional).

   Defines a set of recurrence rules (repeating patterns) for recurring
   calendar objects.

   A JSEvent recurs by applying the recurrence rules to the "start"
   date-time.



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   A JSTask recurs by applying the recurrence rules to the "start" date-
   time, if defined, otherwise it recurs by the "due" date-time, if
   defined.  If the task defines neither a "start" nor "due" date-time,
   it MUST NOT define a "recurrenceRules" property.

   If multiple recurrence rules are given, each rule is to be applied
   and then the union of the results used, ignoring any duplicates.

   A RecurrenceRule object is a JSON object mapping of a RECUR value
   type in iCalendar [RFC5545] [RFC7529] and has the same semantics.  It
   has the following properties:

   o  @type: "String" (mandatory)

      Specifies the type of this object.  This MUST be "RecurrenceRule".

   o  frequency: "String" (mandatory)

      The time span covered by each iteration of this recurrence rule
      (see Section 4.3.2.1 for full semantics).  This MUST be one of the
      following values:

      *  "yearly"

      *  "monthly"

      *  "weekly"

      *  "daily"

      *  "hourly"

      *  "minutely"

      *  "secondly"

      This is the FREQ part from iCalendar, converted to lowercase.

   o  interval: "UnsignedInt" (optional, default: 1)

      The interval of iteration periods at which the recurrence repeats.
      If included, it MUST be an integer >= 1.

      This is the INTERVAL part from iCalendar.

   o  rscale: "String" (optional, default: "gregorian")





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      The calendar system in which this recurrence rule operates, in
      lowercase.  This MUST be either a CLDR-registered calendar system
      name [CLDR], or a vendor-specific value.

      This is the RSCALE part from iCalendar RSCALE [RFC7529], converted
      to lowercase.

   o  skip: "String" (optional, default: "omit")

      The behaviour to use when the expansion of the recurrence produces
      invalid dates.  This property only has an effect if the frequency
      is "yearly" or "monthly".  It MUST be one of the following values:

      *  "omit"

      *  "backward"

      *  "forward"

      This is the SKIP part from iCalendar RSCALE [RFC7529], converted
      to lowercase.

   o  firstDayOfWeek: "String" (optional, default: "mo")

      The day on which the week is considered to start, represented as a
      lowercase abbreviated two-letter English day of the week.  If
      included, it MUST be one of the following values:

      *  "mo"

      *  "tu"

      *  "we"

      *  "th"

      *  "fr"

      *  "sa"

      *  "su"

      This is the WKST part from iCalendar.

   o  byDay: "NDay[]" (optional)

      Days of the week on which to repeat.  An "NDay" object has the
      following properties:



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      *  @type: "String" (mandatory)

         Specifies the type of this object.  This MUST be "NDay".

      *  day: "String" (mandatory)

         A day of the week on which to repeat; the allowed values are
         the same as for the "firstDayOfWeek" RecurrenceRule property.

         This is the day-of-the-week of the BYDAY part in iCalendar,
         converted to lowercase.

      *  nthOfPeriod: "Int" (optional)

         If present, rather than representing every occurrence of the
         weekday defined in the "day" property, it represents only a
         specific instance within the recurrence period.  The value can
         be positive or negative, but MUST NOT be zero.  A negative
         integer means nth-last of period.

         This is the ordinal part of the BYDAY value in iCalendar (e.g.,
         1 or -3).

   o  byMonthDay: "Int[]" (optional)

      Days of the month on which to repeat.  Valid values are between 1
      and the maximum number of days any month may have in the calendar
      given by the "rscale" property, and the negative values of these
      numbers.  For example, in the Gregorian calendar valid values are
      1 to 31 and -31 to -1.  Negative values offset from the end of the
      month.  The array MUST have at least one entry if included.

      This is the BYMONTHDAY part in iCalendar.

   o  byMonth: "String[]" (optional)

      The months in which to repeat.  Each entry is a string
      representation of a number, starting from "1" for the first month
      in the calendar (e.g., "1" means January with the Gregorian
      calendar), with an optional "L" suffix (see [RFC7529]) for leap
      months (this MUST be uppercase, e.g., "3L").  The array MUST have
      at least one entry if included.

      This is the BYMONTH part from iCalendar.

   o  byYearDay: "Int[]" (optional)





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      The days of the year on which to repeat.  Valid values are between
      1 and the maximum number of days any year may have in the calendar
      given by the "rscale" property, and the negative values of these
      numbers.  For example, in the Gregorian calendar valid values are
      1 to 366 and -366 to -1.  Negative values offset from the end of
      the year.  The array MUST have at least one entry if included.

      This is the BYYEARDAY part from iCalendar.

   o  byWeekNo: "Int[]" (optional)

      Weeks of the year in which to repeat.  Valid values are between 1
      and the maximum number of weeks any year may have in the calendar
      given by the "rscale" property, and the negative values of these
      numbers.  For example, in the Gregorian calendar valid values are
      1 to 53 and -53 to -1.  The array MUST have at least one entry if
      included.

      This is the BYWEEKNO part from iCalendar.

   o  byHour: "UnsignedInt[]" (optional)

      The hours of the day in which to repeat.  Valid values are 0 to
      23.  The array MUST have at least one entry if included.  This is
      the BYHOUR part from iCalendar.

   o  byMinute: "UnsignedInt[]" (optional)

      The minutes of the hour in which to repeat.  Valid values are 0 to
      59.  The array MUST have at least one entry if included.

      This is the BYMINUTE part from iCalendar.

   o  bySecond: "UnsignedInt[]" (optional)

      The seconds of the minute in which to repeat.  Valid values are 0
      to 60.  The array MUST have at least one entry if included.

      This is the BYSECOND part from iCalendar.

   o  bySetPosition: "Int[]" (optional)

      The occurrences within the recurrence interval to include in the
      final results.  Negative values offset from the end of the list of
      occurrences.  The array MUST have at least one entry if included.
      This is the BYSETPOS part from iCalendar.

   o  count: "UnsignedInt" (optional)



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      The number of occurrences at which to range-bound the recurrence.
      This MUST NOT be included if an "until" property is specified.

      This is the COUNT part from iCalendar.

   o  until: "LocalDateTime" (optional)

      The date-time at which to finish recurring.  The last occurrence
      is on or before this date-time.  This MUST NOT be included if a
      "count" property is specified.  Note: if not specified otherwise
      for a specific JSCalendar object, this date is to be interpreted
      in the time zone specified in the JSCalendar object's "timeZone"
      property.

      This is the UNTIL part from iCalendar.

4.3.2.1.  Interpreting recurrence rules

   A recurrence rule specifies a set of date-times for recurring
   calendar objects.  A recurrence rule has the following semantics.
   Note, wherever "year", "month" or "day of month" is used, this is
   within the calendar system given by the "rscale" property, which
   defaults to "gregorian" if omitted.

   1.  A set of candidates is generated.  This is every second within a
       period defined by the frequency property value:

       *  "yearly": every second from midnight on the 1st day of a year
          (inclusive) to midnight the 1st day of the following year
          (exclusive).

          If skip is not "omit", the calendar system has leap months and
          there is a byMonth property, generate candidates for the leap
          months even if they don't occur in this year.

          If skip is not "omit" and there is a byMonthDay property,
          presume each month has the maximum number of days any month
          may have in this calendar system when generating candidates,
          even if it's more than this month actually has.

       *  "monthly": every second from midnight on the 1st day of a
          month (inclusive) to midnight on the 1st of the following
          month (exclusive).

          If skip is not "omit" and there is a byMonthDay property,
          presume the month has the maximum number of days any month may
          have in this calendar system when generating candidates, even
          if it's more than this month actually has.



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       *  "weekly": every second from midnight (inclusive) on the first
          day of the week (as defined by the firstDayOfWeek property, or
          Monday if omitted), to midnight 7 days later (exclusive).

       *  "daily": every second from midnight at the start of the day
          (inclusive) to midnight at the end of the day (exclusive).

       *  "hourly": every second from the beginning of the hour
          (inclusive) to the beginning of the next hour (exclusive).

       *  "minutely": every second from the beginning of the minute
          (inclusive) to the beginning of the next minute (exclusive).

       *  "secondly": the second itself, only.

   2.  Each date-time candidate is compared against all of the byX
       properties of the rule except bySetPosition.  If any property in
       the rule does not match the date-time, it is eliminated.  Each
       byX property is an array; the date-time matches the property if
       it matches any of the values in the array.  The properties have
       the following semantics:

       *  byMonth: the date-time is in the given month.

       *  byWeekNo: the date-time is in the nth week of the year.
          Negative numbers mean the nth last week of the year.  This
          corresponds to weeks according to week numbering as defined in
          ISO.8601.2004, with a week defined as a seven day period,
          starting on the firstDayOfWeek property value or Monday if
          omitted.  Week number one of the calendar year is the first
          week that contains at least four days in that calendar year.

          If the date-time is not valid (this may happen when generating
          candidates with a skip property in effect), it is always
          eliminated by this property.

       *  byYearDay: the date-time is on the nth day of year.  Negative
          numbers mean the nth last day of the year.

          If the date-time is not valid (this may happen when generating
          candidates with a skip property in effect), it is always
          eliminated by this property.

       *  byMonthDay: the date-time is on the given day of the month.
          Negative numbers mean the nth last day of the month.

       *  byDay: the date-time is on the given day of the week.  If the
          day is prefixed by a number, it is the nth occurrence of that



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          day of the week within the month (if frequency is monthly) or
          year (if frequency is yearly).  Negative numbers means nth
          last occurrence within that period.

       *  byHour: the date-time has the given hour value.

       *  byMinute: the date-time has the given minute value.

       *  bySecond: the date-time has the given second value.

       If a skip property is defined and is not "omit", there may be
       candidates that do not correspond to valid dates (e.g., 31st
       February in the Gregorian calendar).  In this case, the
       properties MUST be considered in the order above and:

       1.  After applying the byMonth filter, if the candidate's month
           is invalid for the given year, increment it (if skip is
           "forward") or decrement it (if skip is "backward") until a
           valid month is found, incrementing/decrementing the year as
           well if passing through the beginning/end of the year.  This
           only applies to calendar systems with leap months.

       2.  After applying the byMonthDay filter, if the day of the month
           is invalid for the given month and year, change the date to
           the first day of the next month (if skip is "forward") or the
           last day of the current month (if skip is "backward").

       3.  If any valid date produced after applying the skip is already
           a candidate, eliminate the duplicate.  (For example after
           adjusting, 30th February and 31st February would both become
           the same "real" date, so one is eliminated as a duplicate.)

   3.  If a bySetPosition property is included, this is now applied to
       the ordered list of remaining dates.  This property specifies the
       indexes of date-times to keep; all others should be eliminated.
       Negative numbers are indexes from the end of the list, with -1
       being the last item.

   4.  Any date-times before the start date of the event are eliminated
       (see below for why this might be needed).

   5.  If a skip property is included and is not "omit", eliminate any
       date-times that have already been produced by previous iterations
       of the algorithm.  (This is not possible if skip is "omit".)

   6.  If further dates are required (we have not reached the until
       date, or count limit) skip the next (interval - 1) sets of
       candidates, then continue from step 1.



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   When determining the set of occurrence dates for an event or task,
   the following extra rules must be applied:

   1.  The initial date-time to which the rule is applied (the "start"
       date-time for events; the "start" or "due" date-time for tasks)
       is always the first occurrence in the expansion (and is counted
       if the recurrence is limited by a "count" property), even if it
       would normally not match the rule.

   2.  The first set of candidates to consider is that which would
       contain the initial date-time.  This means the first set may
       include candidates before the initial date-time; such candidates
       are eliminated from the results in step (4) as outlined before.

   3.  The following properties MUST be implicitly added to the rule
       under the given conditions:

       *  If frequency is not "secondly" and no bySecond property: Add a
          bySecond property with the sole value being the seconds value
          of the initial date-time.

       *  If frequency is not "secondly" or "minutely", and no byMinute
          property: Add a byMinute property with the sole value being
          the minutes value of the initial date-time.

       *  If frequency is not "secondly", "minutely" or "hourly" and no
          byHour property: Add a byHour property with the sole value
          being the hours value of the initial date-time.

       *  If frequency is "weekly" and no byDay property: Add a byDay
          property with the sole value being the day-of-the-week of the
          initial date-time.

       *  If frequency is "monthly" and no byDay property and no
          byMonthDay property: Add a byMonthDay property with the sole
          value being the day-of-the-month of the initial date-time.

       *  If frequency is "yearly" and no byYearDay property:

          +  If there are no byMonth or byWeekNo properties, and either
             there is a byMonthDay property or there is no byDay
             property: Add a byMonth property with the sole value being
             the month of the initial date-time.

          +  If there is no byMonthDay, byWeekNo or byDay properties:
             Add a byMonthDay property with the sole value being the
             day-of-the-month of the initial date-time.




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          +  If there is a byWeekNo property and no byMonthDay or byDay
             properties: Add a byDay property with the sole value being
             the day-of-the-week of the initial date-time.

4.3.3.  excludedRecurrenceRules

   Type: "RecurrenceRule[]" (optional).

   Defines a set of recurrence rules (repeating patterns) for date-times
   on which the object will not occur.  The rules are interpreted the
   same as for the "recurrenceRules" property (see Section 4.3.2), with
   the exception that the initial date-time to which the rule is applied
   (the "start" date-time for events; the "start" or "due" date-time for
   tasks) is only considered part of the expansion if it matches the
   rule.  The resulting set of date-times are then removed from those
   generated by the recurrenceRules property, as described in
   Section 4.3.

4.3.4.  recurrenceOverrides

   Type: "LocalDateTime[PatchObject]" (optional).

   A map of the recurrence ids (the date-time produced by the recurrence
   rule) to an object of patches to apply to the generated occurrence
   object.

   If the recurrence id does not match a date-time from the recurrence
   rule (or no rule is specified), it is to be treated as an additional
   occurrence (like an RDATE from iCalendar).  The patch object may
   often be empty in this case.

   If the patch object defines the "excluded" property value to be true,
   then the recurring calendar object does not occur at the recurrence
   id date-time (like an EXDATE from iCalendar).  Such a patch object
   MUST NOT patch any other property.

   By default, an occurrence inherits all properties from the main
   object except the start (or due) date-time, which is shifted to match
   the recurrence id LocalDateTime.  However, individual properties of
   the occurrence can be modified by a patch, or multiple patches.  It
   is valid to patch the "start" property value, and this patch takes
   precedence over the value generated from the recurrence id.  Both the
   recurrence id as well as the patched "start" date-time may occur
   before the original JSCalendar object's "start" or "due" date.

   A pointer in the PatchObject MUST be ignored if it starts with one of
   the following prefixes:




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   o  @type

   o  method

   o  privacy

   o  prodId

   o  recurrenceId

   o  recurrenceOverrides

   o  recurrenceRules

   o  relatedTo

   o  replyTo

   o  uid

4.3.5.  excluded

   Type: "Boolean" (optional, default: false).

   Defines if this object is an overridden, excluded instance of a
   recurring JSCalendar object (see Section 4.3.4).  If this property
   value is true, this calendar object instance MUST be removed from the
   occurrence expansion.  The absence of this property or its default
   value false indicates that this instance MUST be included in the
   occurrence expansion.

4.4.  Sharing and Scheduling Properties

4.4.1.  priority

   Type: "Int" (optional, default: 0).

   Specifies a priority for the calendar object.  This may be used as
   part of scheduling systems to help resolve conflicts for a time
   period.

   The priority is specified as an integer in the range 0 to 9.  A value
   of 0 specifies an undefined priority, for which the treatment will
   vary by situation.  A value of 1 is the highest priority.  A value of
   2 is the second highest priority.  Subsequent numbers specify a
   decreasing ordinal priority.  A value of 9 is the lowest priority.
   Other integer values are reserved for future use.




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4.4.2.  freeBusyStatus

   Type: "String" (optional, default: "busy").

   Specifies how this calendar object should be treated when calculating
   free-busy state.  This MUST be one of the following values, a value
   registered in the IANA JSCalendar Enum Registry, or a vendor-specific
   value:

   o  "free": The object should be ignored when calculating whether the
      user is busy.

   o  "busy": The object should be included when calculating whether the
      user is busy.

4.4.3.  privacy

   Type: "String" (optional, default: "public").

   Calendar objects are normally collected together and may be shared
   with other users.  The privacy property allows the object owner to
   indicate that it should not be shared, or should only have the time
   information shared but the details withheld.  Enforcement of the
   restrictions indicated by this property are up to the API via which
   this object is accessed.

   This property MUST NOT affect the information sent to scheduled
   participants; it is only interpreted when the object is shared as
   part of a shared calendar.

   The value MUST be one of the following values, a value registered in
   the IANA JSCalendar Enum Registry, or a vendor-specific value.  Any
   value the client or server doesn't understand should be preserved but
   treated as equivalent to "private".

   o  "public": The full details of the object are visible to those whom
      the object's calendar is shared with.

   o  "private": The details of the object are hidden; only the basic
      time and metadata is shared.  The following properties MAY be
      shared, any other properties MUST NOT be shared:

      *  @type

      *  created

      *  due




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      *  duration

      *  estimatedDuration

      *  freeBusyStatus

      *  privacy

      *  recurrenceOverrides.  Only patches which apply to another
         permissible property are allowed to be shared.

      *  sequence

      *  showWithoutTime

      *  start

      *  timeZone

      *  timeZones

      *  uid

      *  updated

   o  "secret": The object is hidden completely (as though it did not
      exist) when the calendar this object is in is shared.

4.4.4.  replyTo

   Type: "String[String]" (optional).

   Represents methods by which participants may submit their RSVP
   response to the organizer of the calendar object.  The keys in the
   property value are the available methods and MUST only contain ASCII
   alphanumeric characters (A-Za-z0-9).  The value is a URI for the
   method specified in the key.  Future methods may be defined in future
   specifications and registered with IANA; a calendar client MUST
   ignore any method it does not understand, but MUST preserve the
   method key and URI.  This property MUST be omitted if no method is
   defined (rather than being specified as an empty object).

   The following methods are defined:

   o  "imip": The organizer accepts an iMIP [RFC6047] response at this
      email address.  The value MUST be a "mailto:" URI.





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   o  "web": Opening this URI in a web browser will provide the user
      with a page where they can submit a reply to the organizer.

   o  "other": The organizer is identified by this URI but the method
      for submitting the response is undefined.

4.4.5.  participants

   Type: "Id[Participant]" (optional).

   A map of participant ids to participants, describing their
   participation in the calendar object.

   If this property is set and any participant has a sendTo property,
   then the "replyTo" property of this calendar object MUST define at
   least one reply method.

   A Participant object has the following properties:

   o  @type: "String" (mandatory)

      Specifies the type of this object.  This MUST be "Participant".

   o  name: "String" (optional)

      The display name of the participant (e.g., "Joe Bloggs").

   o  email: "String" (optional)

      The email address for the participant.

   o  description: "String" (optional).

      A plain text description of this participant.  For example, this
      may include more information about their role in the event or how
      best to contact them.

   o  sendTo: "String[String]" (optional)

      Represents methods by which the participant may receive the
      invitation and updates to the calendar object.

      The keys in the property value are the available methods and MUST
      only contain ASCII alphanumeric characters (A-Za-z0-9).  The value
      is a URI for the method specified in the key.  Future methods may
      be defined in future specifications and registered with IANA; a
      calendar client MUST ignore any method it does not understand, but
      MUST preserve the method key and URI.  This property MUST be



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      omitted if no method is defined (rather than being specified as an
      empty object).

      The following methods are defined:

      *  "imip": The participant accepts an iMIP [RFC6047] request at
         this email address.  The value MUST be a "mailto:" URI.  It MAY
         be different from the value of the participant's "email"
         property.

      *  "other": The participant is identified by this URI but the
         method for submitting the invitation is undefined.

   o  kind: "String" (optional)

      What kind of entity this participant is, if known.

      This MUST be one of the following values, a value registered in
      the IANA JSCalendar Enum Registry, or a vendor-specific value.
      Any value the client or server doesn't understand should be
      treated the same as if this property is omitted.

      *  "individual": a single person

      *  "group": a collection of people invited as a whole

      *  "location": a physical location that needs to be scheduled,
         e.g., a conference room

      *  "resource": a non-human resource other than a location, such as
         a projector

   o  roles: "String[Boolean]" (mandatory)

      A set of roles that this participant fulfills.

      At least one role MUST be specified for the participant.  The keys
      in the set MUST be one of the following values, a value registered
      in the IANA JSCalendar Enum Registry, or a vendor-specific value:

      *  "owner": The participant is an owner of the object.  This
         signifies they have permission to make changes to it that
         affect the other participants.  Non-owner participants may only
         change properties that just affect themself (for example
         setting their own alerts or changing their rsvp status).

      *  "attendee": The participant is expected to be present at the
         event.



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      *  "optional": The participant's involvement with the event is
         optional.  This is expected to be primarily combined with the
         "attendee" role.

      *  "informational": The participant is copied for informational
         reasons, and is not expected to attend.

      *  "chair": The participant is in charge of the event/task when it
         occurs.

      *  "contact": The participant is someone that may be contacted for
         information about the event.

      The value for each key in the set MUST be true.  It is expected
      that no more than one of the roles "attendee" and "informational"
      be present; if more than one are given, "attendee" takes
      precedence over "informational".  Roles that are unknown to the
      implementation MUST be preserved.

   o  locationId: "String" (optional)

      The location at which this participant is expected to be
      attending.

      If the value does not correspond to any location id in the
      "locations" property of the JSCalendar object, this MUST be
      treated the same as if the participant's locationId were omitted.

   o  language: "String" (optional)

      The language tag as defined in [RFC5646] that best describes the
      participant's preferred language, if known.

   o  participationStatus: "String" (optional, default: "needs-action")

      The participation status, if any, of this participant.

      The value MUST be one of the following values, a value registered
      in the IANA JSCalendar Enum Registry, or a vendor-specific value:

      *  "needs-action": No status yet set by the participant.

      *  "accepted": The invited participant will participate.

      *  "declined": The invited participant will not participate.

      *  "tentative": The invited participant may participate.




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      *  "delegated": The invited participant has delegated their
         attendance to another participant, as specified in the
         delegatedTo property.

   o  participationComment: "String" (optional)

      A note from the participant to explain their participation status.

   o  expectReply: "Boolean" (optional, default: false)

      If true, the organizer is expecting the participant to notify them
      of their participation status.

   o  scheduleAgent: "String" (optional, default: "server")

      Who is responsible for sending scheduling messages with this
      calendar object to the participant.

      The value MUST be one of the following values, a value registered
      in the IANA JSCalendar Enum Registry, or a vendor-specific value:

      *  "server": The calendar server will send the scheduling
         messages.

      *  "client": The calendar client will send the scheduling
         messages.

      *  "none": No scheduling messages are to be sent to this
         participant.

   o  scheduleForceSend: "Boolean" (optional, default: false)

      A client may set the property on a participant to true to request
      that the server send a scheduling message to the participant when
      it would not normally do so (e.g. if no significant change is made
      the object or the scheduleAgent is set to client).  The property
      MUST NOT be stored in the JSCalendar object on the server or
      appear in a scheduling message.

   o  scheduleSequence: "UnsignedInt" (optional, default: 0)

      The sequence number of the last response from the participant.  If
      defined, this MUST be a non-negative integer.

      This can be used to determine whether the participant has sent a
      new RSVP following significant changes to the calendar object, and
      to determine if future responses are responding to a current or
      older view of the data.



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   o  scheduleStatus: "String[]" (optional)

      A list of status codes, as defined in Section 3.8.8.3 of
      [RFC5545], returned from the processing of the most recent
      scheduling message sent to this participant.

      Servers MUST only add or change this property when they send a
      scheduling message to the participant.  Clients SHOULD NOT change
      or remove this property if it was provided by the server.  Clients
      MAY add, change, or remove the property for participants where the
      client is handling the scheduling.

      This property MUST NOT be included in scheduling messages.

   o  scheduleUpdated: "UTCDateTime" (optional)

      The timestamp for the most recent response from this participant.

      This is the "updated" property of the last response when using
      iTIP.  It can be compared to the "updated" property in future
      responses to detect and discard older responses delivered out of
      order.

   o  invitedBy: "String" (optional)

      The participant id of the participant who invited this one, if
      known.

   o  delegatedTo: "String[Boolean]" (optional)

      A set of participant ids that this participant has delegated their
      participation to.  Each key in the set MUST be the id of a
      participant.  The value for each key in the set MUST be true.  If
      there are no delegates, this MUST be omitted (rather than
      specified as an empty set).

   o  delegatedFrom: "String[Boolean]" (optional)

      A set of participant ids that this participant is acting as a
      delegate for.  Each key in the set MUST be the id of a
      participant.  The value for each key in the set MUST be true.  If
      there are no delegators, this MUST be omitted (rather than
      specified as an empty set).

   o  memberOf: "String[Boolean]" (optional)

      A set of group participants that were invited to this calendar
      object, which caused this participant to be invited due to their



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      membership in the group(s).  Each key in the set MUST be the id of
      a participant.  The value for each key in the set MUST be true.
      If there are no groups, this MUST be omitted (rather than
      specified as an empty set).

   o  linkIds: "String[Boolean]" (optional)

      A set of links to more information about this participant, for
      example in vCard format.  The keys in the set MUST be the id of a
      Link object in the calendar object's "links" property.  The value
      for each key in the set MUST be true.  If there are no links, this
      MUST be omitted (rather than specified as an empty set).

   o  progress: "String" (optional; only allowed for participants of a
      JSTask).  Represents the progress of the participant for this
      task.  It MUST NOT be set if the "participationStatus" of this
      participant is any value other than "accepted".  See Section 5.2.5
      for allowed values and semantics.

   o  progressUpdated: "UTCDateTime" (optional; only allowed for
      participants of a JSTask).  Specifies the date-time the progress
      property was last set on this participant.  See Section 5.2.6 for
      allowed values and semantics.

   o  percentComplete: "UnsignedInt" (optional; only allowed for
      participants of a JSTask).  Represents the percent completion of
      the participant for this task.  The property value MUST be a
      positive integer between 0 and 100.

4.5.  Alerts Properties

4.5.1.  useDefaultAlerts

   Type: "Boolean" (optional, default: false).

   If true, use the user's default alerts and ignore the value of the
   "alerts" property.  Fetching user defaults is dependent on the API
   from which this JSCalendar object is being fetched, and is not
   defined in this specification.  If an implementation cannot determine
   the user's default alerts, or none are set, it MUST process the
   alerts property as if "useDefaultAlerts" is set to false.

4.5.2.  alerts

   Type: "Id[Alert]" (optional).

   A map of alert ids to Alert objects, representing alerts/reminders to
   display or send to the user for this calendar object.



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   An Alert Object has the following properties:

   o  @type: "String" (mandatory)

      Specifies the type of this object.  This MUST be "Alert".

   o  trigger: "OffsetTrigger|AbsoluteTrigger|UnknownTrigger"
      (mandatory)

      Defines when to trigger the alert.  New types may be defined in
      future documents.

      An "OffsetTrigger" object has the following properties:

      *  @type: "String" (mandatory)

         Specifies the type of this object.  This MUST be
         "OffsetTrigger".

      *  offset: "SignedDuration" (mandatory).

         Defines the offset at which to trigger the alert relative to
         the time property defined in the "relativeTo" property of the
         alert.  Negative durations signify alerts before the time
         property, positive durations signify alerts after.

      *  relativeTo: "String" (optional, default: "start")

         Specifies the time property that the alert offset is relative
         to.  The value MUST be one of:

         +  "start": triggers the alert relative to the start of the
            calendar object

         +  "end": triggers the alert relative to the end/due time of
            the calendar object

      An "AbsoluteTrigger" object has the following properties:

      *  @type: "String" (mandatory)

         Specifies the type of this object.  This MUST be
         "AbsoluteTrigger".

      *  when: "UTCDateTime" (mandatory).

         Defines a specific UTC date-time when the alert is triggered.




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      An "UnknownTrigger" object is an object that contains a "@type"
      property whose value is not recognized (i.e., not "OffsetTrigger"
      or "AbsoluteTrigger"), plus zero or more other properties.  This
      is for compatibility with client extensions and future
      specifications.  Implementations SHOULD NOT trigger for trigger
      types they do not understand, but MUST preserve them.

   o  acknowledged: "UTCDateTime" (optional)

      This records when an alert was last acknowledged.  This is set
      when the user has dismissed the alert; other clients that sync
      this property SHOULD automatically dismiss or suppress duplicate
      alerts (alerts with the same alert id that triggered on or before
      this date-time).

      For a recurring calendar object, the "acknowledged" property of
      the parent object MUST be updated, unless the alert is already
      overridden in the "recurrenceOverrides" property.

      Certain kinds of alert action may not provide feedback as to when
      the user sees them, for example email based alerts.  For those
      kinds of alerts, this property SHOULD be set immediately when the
      alert is triggered and the action successfully carried out.

   o  relatedTo: "String[Relation]" (optional)

      Relates this alert to other alerts in the same JSCalendar object.
      If the user wishes to snooze an alert, the application SHOULD
      create an alert to trigger after snoozing.  All snooze alerts
      SHOULD set a relation to the identifier of the original alert.
      The Relation object SHOULD set the "parent" relation type.

   o  action: "String" (optional, default: "display")

      Describes how to alert the user.

      The value MUST be at most one of the following values, a value
      registered in the IANA JSCalendar Enum Registry, or a vendor-
      specific value:

      *  "display": The alert should be displayed as appropriate for the
         current device and user context.

      *  "email": The alert should trigger an email sent out to the
         user, notifying about the alert.  This action is typically only
         appropriate for server implementations.





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4.6.  Multilingual Properties

4.6.1.  localizations

   Type: "String[PatchObject]" (optional).

   A map of language tags [RFC5646] to patch objects, which localize the
   calendar object into the locale of the respective language tag.

   See the description of PatchObject (Section 1.4.8) for the structure
   of the PatchObject.  The patches are applied to the top-level
   calendar object.  In addition, the "locale" property of the patched
   object is set to the language tag.  All pointers for patches MUST end
   with one of the following suffixes; any patch that does not follow
   this MUST be ignored unless otherwise specified in a future RFC:

   o  title

   o  description

   o  name

   A patch MUST NOT have the prefix "recurrenceOverrides"; any
   localization of the override MUST be a patch to the localizations
   property inside the override instead.  For example, a patch to
   "locations/abcd1234/title" is permissible, but a patch to "uid" or
   "recurrenceOverrides/2018-01-05T14:00:00/title" is not.

   Note that this specification does not define how to maintain validity
   of localized content.  For example, a client application changing a
   JSCalendar object's title property might also need to update any
   localizations of this property.  Client implementations SHOULD
   provide the means to manage localizations, but how to achieve this is
   specific to the application's workflow and requirements.

4.7.  Time Zone Properties

4.7.1.  timeZone

   Type: "String|null" (optional, default: null).

   Identifies the time zone the object is scheduled in, or null for
   floating time.  This is either a name from the IANA Time Zone
   Database [TZDB] or the id of a custom time zone from the "timeZones"
   property (see Section 1.4.9).  If omitted, this MUST be presumed to
   be null (i.e., floating time).





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4.7.2.  timeZones

   Type: "String[TimeZone]" (optional).

   Maps identifiers of custom time zones to their time zone definitions.
   The following restrictions apply for each key in the map:

   o  It MUST start with the "/" character (ASCII decimal 47; also see
      Sections 3.2.19 of [RFC5545] and 3.6. of [RFC7808] for discussion
      of the forward slash character in time zone identifiers).

   o  It MUST be a valid "paramtext" value as specified in Section 3.1.
      of [RFC5545].

   o  At least one other property in the same JSCalendar object MUST
      reference a time zone using this identifier (i.e., orphaned time
      zones are not allowed).

   An identifier need only be unique to this JSCalendar object.  A
   JSCalendar object may be part in a hierarchy of other JSCalendar
   objects (say, a JSEvent is an entry in a JSGroup).  In this case, the
   set of time zones is the sum of the time zone definitions of this
   object and its parent objects.  If multiple time zones with the same
   identifier exist, then the definition closest to the calendar object
   in relation to its parents MUST be used.  (In context of JSEvent, a
   time zone definition in its timeZones property has precedence over a
   definition of the same id in the JSGroup).  Time zone definitions in
   any children of the calendar object MUST be ignored.

   A TimeZone object maps a VTIMEZONE component from iCalendar [RFC5545]
   and the semantics are as defined there.  A valid time zone MUST
   define at least one transition rule in the "standard" or "daylight"
   property.  Its properties are:

   o  @type: "String" (mandatory)

      Specifies the type of this object.  This MUST be "TimeZone".

   o  tzId: "String" (mandatory).

      The TZID property from iCalendar.

   o  updated: "UTCDateTime" (optional)

      The LAST-MODIFIED property from iCalendar.

   o  url: "String" (optional)




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      The TZURL property from iCalendar.

   o  validUntil: "UTCDateTime" (optional)

      The TZUNTIL property from iCalendar specified in [RFC7808].

   o  aliases: "String[Boolean]" (optional)

      Maps the TZID-ALIAS-OF properties from iCalendar specified in
      [RFC7808] to a JSON set of aliases.  The set is represented as an
      object, with the keys being the aliases.  The value for each key
      in the set MUST be true.

   o  standard: "TimeZoneRule[]" (optional)

      The STANDARD sub-components from iCalendar.  The order MUST be
      preserved during conversion.

   o  daylight: "TimeZoneRule[]" (optional).

      The DAYLIGHT sub-components from iCalendar.  The order MUST be
      preserved during conversion.

   A TimeZoneRule object maps a STANDARD or DAYLIGHT sub-component from
   iCalendar, with the restriction that at most one recurrence rule is
   allowed per rule.  It has the following properties:

   o  @type: "String" (mandatory)

      Specifies the type of this object.  This MUST be "TimeZoneRule".

   o  start: "LocalDateTime" (mandatory)

      The DTSTART property from iCalendar.

   o  offsetTo: "String" (mandatory)

      The TZOFFSETTO property from iCalendar.

   o  offsetFrom: "String" (mandatory)

      The TZOFFSETFROM property from iCalendar.

   o  recurrenceRules: "RecurrenceRule[]" (optional)

      The RRULE property mapped as specified in Section 4.3.2.  During
      recurrence rule evaluation, the "until" property value MUST be
      interpreted as a local time in the UTC time zone.



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   o  recurrenceOverrides: "LocalDateTime[PatchObject]" (optional)

      Maps the RDATE properties from iCalendar.  The set is represented
      as an object, with the keys being the recurrence dates.  The patch
      object MUST be empty.

   o  names: "String[Boolean]" (optional)

      Maps the TZNAME properties from iCalendar to a JSON set.  The set
      is represented as an object, with the keys being the names.  The
      value for each key in the set MUST be true.

   o  comments: "String[]" (optional).  Maps the COMMENT properties from
      iCalendar.  The order MUST be preserved during conversion.

5.  Type-specific JSCalendar Properties

5.1.  JSEvent Properties

   In addition to the common JSCalendar object properties (Section 4) a
   JSEvent has the following properties:

5.1.1.  start

   Type: "LocalDateTime" (mandatory).

   The date/time the event starts in the event's time zone (as specified
   in the "timeZone" property, see Section 4.7.1).

5.1.2.  duration

   Type: "Duration" (optional, default: "PT0S").

   The zero or positive duration of the event in the event's start time
   zone.

   A JSEvent MAY involve start and end locations that are in different
   time zones (e.g., a trans-continental flight).  This can be expressed
   using the "relativeTo" and "timeZone" properties of the JSEvent's
   Location objects (see Section 4.2.5).

5.1.3.  status

   Type: "String" (optional, default: "confirmed").

   The scheduling status (Section 4.4) of a JSEvent.  If set, it MUST be
   one of the following values, a value registered in the IANA
   JSCalendar Enum Registry, or a vendor-specific value:



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   o  "confirmed": Indicates the event is definitely happening.

   o  "cancelled": Indicates the event has been cancelled.

   o  "tentative": Indicates the event may happen.

5.2.  JSTask Properties

   In addition to the common JSCalendar object properties (Section 4) a
   JSTask has the following properties:

5.2.1.  due

   Type: "LocalDateTime" (optional).

   The date/time the task is due in the task's time zone.

5.2.2.  start

   Type: "LocalDateTime" (optional).

   The date/time the task should start in the task's time zone.

5.2.3.  estimatedDuration

   Type: "Duration" (optional).

   Specifies the estimated positive duration of time the task takes to
   complete.

5.2.4.  percentComplete

   Type: "UnsignedInt" (optional).

   Represents the percent completion of the task overall.  The property
   value MUST be a positive integer between 0 and 100.

5.2.5.  progress

   Type: "String" (optional).

   Defines the progress of this task.  If omitted, the default progress
   (Section 4.4) of a JSTask is defined as follows (in order of
   evaluation):

   o  "completed": if the "progress" property value of all participants
      is "completed".




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   o  "failed": if at least one "progress" property value of a
      participant is "failed".

   o  "in-process": if at least one "progress" property value of a
      participant is "in-process".

   o  "needs-action": If none of the other criteria match.

   If set, it MUST be one of the following values, a value registered in
   the IANA JSCalendar Enum Registry, or a vendor-specific value:

   o  "needs-action": Indicates the task needs action.

   o  "in-process": Indicates the task is in process.

   o  "completed": Indicates the task is completed.

   o  "failed": Indicates the task failed.

   o  "cancelled": Indicates the task was cancelled.

5.2.6.  progressUpdated

   Type: "UTCDateTime" (optional).

   Specifies the date/time the "progress" property of either the task
   overall (Section 5.2.5) or a specific participant (Section 4.4.5) was
   last updated.

   If the task is recurring and has future instances, a client may want
   to keep track of the last progress update timestamp of a specific
   task recurrence, but leave other instances unchanged.  One way to
   achieve this is by overriding the progressUpdated property in the
   task "recurrenceOverrides" property.  However, this could produce a
   long list of timestamps for regularly recurring tasks.  An
   alternative approach is to split the JSTask into a current, single
   instance of JSTask with this instance progress update time and a
   future recurring instance.  See also Section 4.1.3 on splitting.

5.3.  JSGroup Properties

   JSGroup supports the following common JSCalendar properties
   (Section 4):

   o  @type

   o  categories




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   o  color

   o  created

   o  description

   o  descriptionContentType

   o  keywords

   o  links

   o  locale

   o  prodId

   o  timeZones

   o  title

   o  updated

   o  uid

   In addition, the following JSGroup-specific properties are supported:

5.3.1.  entries

   Type: "(JSTask|JSEvent)[]" (mandatory).

   A collection of group members.  Implementations MUST ignore entries
   of unknown type.

5.3.2.  source

   Type: "String" (optional).

   The source from which updated versions of this group may be retrieved
   from.  The value MUST be a URI.

6.  Examples

   The following examples illustrate several aspects of the JSCalendar
   data model and format.  The examples may omit mandatory or additional
   properties, which is indicated by a placeholder property with key
   "...".  While most of the examples use calendar event objects, they
   are also illustrative for tasks.




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6.1.  Simple event

   This example illustrates a simple one-time event.  It specifies a
   one-time event that begins on January 15, 2018 at 1pm New York local
   time and ends after 1 hour.

   {
     "@type": "jsevent",
     "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f1",
     "updated": "2018-01-15T18:00:00Z",
     "title": "Some event",
     "start": "2018-01-15T13:00:00",
     "timeZone": "America/New_York",
     "duration": "PT1H"
   }

6.2.  Simple task

   This example illustrates a simple task for a plain to-do item.

   {
     "@type": "jstask",
     "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f2",
     "updated": "2018-01-15T18:00:00Z",
     "title": "Do something"
   }

6.3.  Simple group

   This example illustrates a simple calendar object group that contains
   an event and a task.




















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   {
     "@type": "jsgroup",
     "uid": "2a358cee-6489-4f14-a57f-c104db4dc343",
     "updated": "2018-01-15T18:00:00Z",
     "name": "A simple group",
     "entries": [{
       "@type": "jsevent",
       "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f1",
       "updated": "2018-01-15T18:00:00Z",
       "title": "Some event",
       "start": "2018-01-15T13:00:00",
       "timeZone": "America/New_York",
       "duration": "PT1H"
     },
     "2a358cee-6489-4f14-a57f-c104db4dc2f2": {
       "@type": "jstask",
       "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f2",
       "updated": "2018-01-15T18:00:00Z",
       "title": "Do something"
     }]
   }

6.4.  All-day event

   This example illustrates an event for an international holiday.  It
   specifies an all-day event on April 1 that occurs every year since
   the year 1900.

   {
     "...": "",
     "title": "April Fool's Day",
     "showWithoutTime": true,
     "start": "1900-04-01T00:00:00",
     "duration": "P1D",
     "recurrenceRules": [{
       "@type": "RecurrenceRule",
       "frequency": "yearly"
     }]
   }

6.5.  Task with a due date

   This example illustrates a task with a due date.  It is a reminder to
   buy groceries before 6pm Vienna local time on January 19, 2018.  The
   calendar user expects to need 1 hour for shopping.






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   {
     "...": "",
     "title": "Buy groceries",
     "due": "2018-01-19T18:00:00",
     "timeZone": "Europe/Vienna",
     "estimatedDuration": "PT1H"
   }

6.6.  Event with end time zone

   This example illustrates the use of end time zones by use of an
   international flight.  The flight starts on April 1, 2018 at 9am in
   Berlin local time.  The duration of the flight is scheduled at 10
   hours 30 minutes.  The time at the flight's destination is in the
   same time zone as Tokyo.  Calendar clients could use the end time
   zone to display the arrival time in Tokyo local time and highlight
   the time zone difference of the flight.  The location names can serve
   as input for navigation systems.

   {
     "...": "",
     "title": "Flight XY51 to Tokyo",
     "start": "2018-04-01T09:00:00",
     "timeZone": "Europe/Berlin",
     "duration": "PT10H30M",
     "locations": {
       "2a358cee-6489-4f14-a57f-c104db4dc2f1": {
         "@type": "Location",
         "rel": "start",
         "name": "Frankfurt Airport (FRA)"
       },
       "c2c7ac67-dc13-411e-a7d4-0780fb61fb08": {
         "@type": "Location",
         "rel": "end",
         "name": "Narita International Airport (NRT)",
         "timeZone": "Asia/Tokyo"
       }
     }
   }

6.7.  Floating-time event (with recurrence)

   This example illustrates the use of floating time.  Since January 1,
   2018, a calendar user blocks 30 minutes every day to practice Yoga at
   7am local time, in whatever time zone the user is located on that
   date.





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   {
     "...": "",
     "title": "Yoga",
     "start": "2018-01-01T07:00:00",
     "duration": "PT30M",
     "recurrenceRules": [{
       "@type": "RecurrenceRule",
       "frequency": "daily"
     }]
   }

6.8.  Event with multiple locations and localization

   This example illustrates an event that happens at both a physical and
   a virtual location.  Fans can see a live concert on premises or
   online.  The event title and descriptions are localized.



































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   {
     "...": "",
     "title": "Live from Music Bowl: The Band",
     "description": "Go see the biggest music event ever!",
     "locale": "en",
     "start": "2018-07-04T17:00:00",
     "timeZone": "America/New_York",
     "duration": "PT3H",
     "locations": {
       "c0503d30-8c50-4372-87b5-7657e8e0fedd": {
         "@type": "Location",
         "name": "The Music Bowl",
         "description": "Music Bowl, Central Park, New York",
         "coordinates": "geo:40.7829,-73.9654"
       }
     },
     "virtualLocations": {
       "6f3696c6-1e07-47d0-9ce1-f50014b0041a": {
         "@type": "VirtualLocation",
         "name": "Free live Stream from Music Bowl",
         "uri": "https://stream.example.com/the_band_2018"
       }
     },
     "localizations": {
       "de": {
         "title": "Live von der Music Bowl: The Band!",
         "description": "Schau dir das groesste Musikereignis an!",
         "virtualLocations/6f3696c6-1e07-47d0-9ce1-f50014b0041a/name":
                                 "Gratis Live-Stream aus der Music Bowl"
       }
     }
   }

6.9.  Recurring event with overrides

   This example illustrates the use of recurrence overrides.  A math
   course at a University is held for the first time on January 8, 2018
   at 9am London time and occurs every week until June 25, 2018.  Each
   lecture lasts for one hour and 30 minutes and is located at the
   Mathematics department.  This event has exceptional occurrences: at
   the last occurrence of the course is an exam, which lasts for 2 hours
   and starts at 10am.  Also, the location of the exam differs from the
   usual location.  On April 2 no course is held.  On January 5 at 2pm
   is an optional introduction course, that occurs before the first
   regular lecture.






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   {
     "...": "",
     "title": "Calculus I",
     "start": "2018-01-08T09:00:00",
     "timeZone": "Europe/London",
     "duration": "PT1H30M",
     "locations": {
       "2a358cee-6489-4f14-a57f-c104db4dc2f1": {
         "@type": "Location",
         "title": "Math lab room 1",
         "description": "Math Lab I, Department of Mathematics"
       }
     },
     "recurrenceRules": [{
       "@type": "RecurrenceRule",
       "frequency": "weekly",
       "until": "2018-06-25T09:00:00"
     }],
     "recurrenceOverrides": {
       "2018-01-05T14:00:00": {
         "title": "Introduction to Calculus I (optional)"
       },
       "2018-04-02T09:00:00": {
         "excluded": "true"
       },
       "2018-06-25T09:00:00": {
         "title": "Calculus I Exam",
         "start": "2018-06-25T10:00:00",
         "duration": "PT2H",
         "locations": {
           "2a358cee-6489-4f14-a57f-c104db4dc2f1": {
             "@type": "Location",
             "title": "Big Auditorium",
             "description": "Big Auditorium, Other Road"
           }
         }
       }
     }
   }

6.10.  Recurring event with participants

   This example illustrates scheduled events.  A team meeting occurs
   every week since January 8, 2018 at 9am Johannesburg time.  The event
   owner also chairs the event.  Participants meet in a virtual meeting
   room.  An attendee has accepted the invitation, but on March 8, 2018
   he is unavailable and declined participation for this occurrence.




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   {
     "...": "",
     "title": "FooBar team meeting",
     "start": "2018-01-08T09:00:00",
     "timeZone": "Africa/Johannesburg",
     "duration": "PT1H",
     "virtualLocations": {
       "2a358cee-6489-4f14-a57f-c104db4dc2f1": {
         "@type": "VirtualLocation",
         "name": "ChatMe meeting room",
         "uri": "https://chatme.example.com?id=1234567"
       }
     },
     "recurrenceRules": [{
       "@type": "RecurrenceRule",
       "frequency": "weekly"
     }],
     "replyTo": {
       "imip": "mailto:6489-4f14-a57f-c1@schedule.example.com"
     },
     "participants": {
       "dG9tQGZvb2Jhci5xlLmNvbQ": {
         "@type": "Participant",
         "name": "Tom Tool",
         "email": "tom@foobar.example.com",
         "sendTo": {
           "imip": "mailto:6489-4f14-a57f-c1@calendar.example.com"
         },
         "participationStatus": "accepted",
         "roles": {
           "attendee": true
         }
       },
       "em9lQGZvb2GFtcGxlLmNvbQ": {
         "@type": "Participant",
         "name": "Zoe Zelda",
         "email": "zoe@foobar.example.com",
         "sendTo": {
           "imip": "mailto:zoe@foobar.example.com"
         },
         "participationStatus": "accepted",
         "roles": {
           "owner": true,
           "attendee": true,
           "chair": true
         }
       },
       "...": ""



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     },
     "recurrenceOverrides": {
       "2018-03-08T09:00:00": {
         "participants/dG9tQGZvb2Jhci5xlLmNvbQ/participationStatus":
                                                             "declined"
       }
     }
   }

7.  Security Considerations

   Calendaring and scheduling information is very privacy-sensitive.
   Its transmission must be done carefully to protect it from possible
   threats, such as eavesdropping, replay, message insertion, deletion,
   modification, and man-in-the-middle attacks.

   The data being stored and transmitted may be used in systems with
   real world consequences.  For example, a home automation system may
   turn an alarm on and off.  Or a coworking space may charge money to
   the organiser of an event that books one of their meeting rooms.
   Such systems must be careful to authenticate all data they receive to
   prevent them from being subverted.

   This document just defines the data format; such considerations are
   primarily the concern of the API or method of storage and
   transmission of such files.

7.1.  Expanding Recurrences

   A recurrence rule may produce infinite occurrences of an event.
   Implementations MUST handle expansions carefully to prevent
   accidental or deliberate resource exhaustion.

   Conversely, a recurrence rule may be specified that does not expand
   to anything.  It is not always possible to tell this through static
   analysis of the rule, so implementations MUST be careful to avoid
   getting stuck in infinite loops, or otherwise exhausting resources
   while searching for the next occurrence.

7.2.  JSON Parsing

   The Security Considerations of [RFC8259] apply to the use of JSON as
   the data interchange format.

   As for any serialization format, parsers need to thoroughly check the
   syntax of the supplied data.  JSON uses opening and closing tags for
   several types and structures, and it is possible that the end of the
   supplied data will be reached when scanning for a matching closing



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   tag; this is an error condition, and implementations need to stop
   scanning at the end of the supplied data.

   JSON also uses a string encoding with some escape sequences to encode
   special characters within a string.  Care is needed when processing
   these escape sequences to ensure that they are fully formed before
   the special processing is triggered, with special care taken when the
   escape sequences appear adjacent to other (non-escaped) special
   characters or adjacent to the end of data (as in the previous
   paragraph).

   If parsing JSON into a non-textual structured data format,
   implementations may need to allocate storage to hold JSON string
   elements.  Since JSON does not use explicit string lengths, the risk
   of denial of service due to resource exhaustion is small, but
   implementations may still wish to place limits on the size of
   allocations they are willing to make in any given context, to avoid
   untrusted data causing excessive memory allocation.

7.3.  URI Values

   Several JSCalendar properties contain URIs as values, and processing
   these properties requires extra care.  Section 7 of [RFC3986]
   discusses security risks related to URIs.

   A maliciously constructed JSCalendar object may contain a very large
   number of URIs.  In the case of published calendars with a large
   number of subscribers, such objects could be widely distributed.
   Implementations should be careful to limit the automatic fetching of
   linked resources to reduce the risk of this being an amplification
   vector for a denial-of-service attack.

7.4.  Spam

   Calendar systems may receive JSCalendar files from untrusted sources,
   in particular as attachments to emails.  This can be a vector for an
   attacker to inject spam into a user's calendar.  This may confuse,
   annoy, and mislead users, or overwhelm their calendar with bogus
   events, preventing them from seeing legitimate ones.

   Heuristic, statistical or machine-learning-based filters can be
   effective in filtering out spam.  Authentication mechanisms such as
   DKIM [RFC6376] can help establish the source of messages and
   associate the data with existing relationships (such as an address
   book contact).  Misclassifications are always possible however, and
   providing a feedback mechanism for users to quickly correct this is
   advised.




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7.5.  Duplication

   It is important for calendar systems to maintain the UID of an event
   when updating it to avoid unexpected duplication of events.  When the
   UID changes, consumers of the data may not remove the previous
   version of the event if it has a different UID.  This can lead to a
   confusing situation for the user, with many variations of the event
   and no indication of which one is correct.  Care must be taken by
   consumers of the data to remove old events where possible to avoid an
   accidental denial-of-service attack due to the volume of data.

7.6.  Time Zones

   Events recur in a particular time zone.  When this differs from the
   user's current time zone, it may unexpectedly cause an occurrence to
   shift in time for that user due to a daylight savings change in the
   event's time zone.  A maliciously crafted event could attempt to
   confuse users with such an event to ensure a meeting is missed.

8.  IANA Considerations

8.1.  Media Type Registration

   This document defines a media type for use with JSCalendar data
   formatted in JSON.

   Type name:  application

   Subtype name:  jscalendar+json

   Required parameters:  type

      The "type" parameter conveys the type of the JSCalendar data in
      the body part, with the value being one of "jsevent", "jstask", or
      "jsgroup".  The parameter MUST NOT occur more than once.  It MUST
      match the value of the "@type" property of the JSON-formatted
      JSCalendar object in the body.

   Optional parameters:  none

   Encoding considerations:  Same as encoding considerations of
      application/json as specified in RFC8529, Section 11 [RFC8259].

   Security considerations:  See Section 7 of this document.

   Interoperability considerations:  This media type provides an
      alternative to iCalendar, jCal and proprietary JSON-based
      calendaring data formats.



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   Published specification:  This specification.

   Applications that use this media type:  Applications that currently
      make use of the text/calendar and application/calendar+json media
      types can use this as an alternative.  Similarly, applications
      that use the application/json media type to transfer calendaring
      data can use this to further specify the content.

   Fragment identifier considerations:  N/A

   Additional information:

      Magic number(s):  N/A

      File extensions(s):  N/A

      Macintosh file type code(s):  N/A

   Person & email address to contact for further information:
      calsify@ietf.org

   Intended usage:  COMMON

   Restrictions on usage:  N/A

   Author:  See the "Author's Address" section of this document.

   Change controller:  IETF

8.2.  Creation of "JSCalendar Properties" Registry

   The IANA will create the "JSCalendar Properties" registry to allow
   interoperability of extensions to JSCalendar objects.

   This registry follows the Expert Review process ([RFC8126],
   Section 4.5).  If the "intended use" field is "common", sufficient
   documentation is required to enable interoperability.  Preliminary
   community review for this registry is optional but strongly
   encouraged.

   A registration can have an intended use of "common", "reserved", or
   "obsolete".  The IANA will list common-use registrations prominently
   and separately from those with other intended use values.

   A "reserved" registration reserves a property name without assigning
   semantics to avoid name collisions with future extensions or protocol
   use.




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   An "obsolete" registration denotes a property that is no longer
   expected to be added by up-to-date systems.  A new property has
   probably been defined covering the obsolete property's semantics.

   The JSCalendar property registration procedure is not a formal
   standards process but rather an administrative procedure intended to
   allow community comment and sanity checking without excessive time
   delay.  It is designed to encourage vendors to document and register
   new properties they add for use cases not covered by the original
   standard, leading to increased interoperability.

8.2.1.  Preliminary Community Review

   Notice of a potential new registration SHOULD be sent to the Calext
   mailing list <calsify@ietf.org> for review.  This mailing list is
   appropriate to solicit community feedback on a proposed new property.

   Properties registrations must be marked with their intended use:
   "common", "reserved" or "obsolete".

   The intent of the public posting to this list is to solicit comments
   and feedback on the choice of the property name, the unambiguity of
   the specification document, and a review of any interoperability or
   security considerations.  The submitter may submit a revised
   registration proposal or abandon the registration completely at any
   time.

8.2.2.  Submit Request to IANA

   Registration requests can be sent to <iana@iana.org>.

8.2.3.  Designated Expert Review

   The primary concern of the designated expert (DE) is preventing name
   collisions and encouraging the submitter to document security and
   privacy considerations.  For a common-use registration, the DE is
   expected to confirm that suitable documentation, as described in
   Section 4.6 of [RFC8126], is available to ensure interoperability.
   That documentation will usually be in an RFC, but simple definitions
   are likely to use a web/wiki page, and if a sentence or two is deemed
   sufficient it could be described in the registry itself.  The DE
   should also verify that the property name does not conflict with work
   that is active or already published within the IETF.  A published
   specification is not required for reserved or obsolete registrations.

   The DE will either approve or deny the registration request and
   publish a notice of the decision to the Calext WG mailing list or its
   successor, as well as inform IANA.  A denial notice must be justified



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   by an explanation, and, in the cases where it is possible, concrete
   suggestions on how the request can be modified so as to become
   acceptable should be provided.

8.2.4.  Change Procedures

   Once a JSCalendar property has been published by the IANA, the change
   controller may request a change to its definition.  The same
   procedure that would be appropriate for the original registration
   request is used to process a change request.

   JSCalendar property registrations may not be deleted; properties that
   are no longer believed appropriate for use can be declared obsolete
   by a change to their "intended use" field; such properties will be
   clearly marked in the lists published by the IANA.

   Significant changes to a JSCalendar property's definition should be
   requested only when there are serious omissions or errors in the
   published specification, as such changes may cause interoperability
   issues.  When review is required, a change request may be denied if
   it renders entities that were valid under the previous definition
   invalid under the new definition.

   The owner of a JSCalendar property may pass responsibility to another
   person or agency by informing the IANA; this can be done without
   discussion or review.

8.2.5.  JSCalendar Properties Registry Template

   o  Property Name: The name of the property.  The property name MUST
      NOT already be registered for any of the object types listed in
      the "Property Context" field of this registration.  Other object
      types MAY already have registered a different property with the
      same name.

   o  Property Type: The type of this property, using type signatures as
      specified in Section 1.3.  The property type MUST be registed in
      the Type Registry.

   o  Property Context: A comma-separated list of JSCalendar object
      types this property is allowed on.

   o  Reference or Description: A brief description or RFC number and
      section reference where the property is specified (omitted for
      "reserved" property names).

   o  Intended Use: Common, reserved, or obsolete.




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   o  Change Controller: ("IETF" for IETF-stream RFCs).

8.2.6.  Initial Contents for the JSCalendar Properties Registry

   The following table lists the initial entries of the JSCalendar
   Properties registry.  All properties are for common-use.  All RFC
   section references are for this document.  The change controller for
   all these properties is "IETF".

   +---------------+----------------------------+------------+---------+
   | Property Name | Property Type              | Property   | Referen |
   |               |                            | Context    | ce or D |
   |               |                            |            | escript |
   |               |                            |            | ion     |
   +---------------+----------------------------+------------+---------+
   | @type         | String                     | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.1.1, |
   |               |                            | JSGroup, A | Section |
   |               |                            | bsoluteTri |  4.5.2, |
   |               |                            | gger,      | Section |
   |               |                            | Alert,     |  4.2.7, |
   |               |                            | Link,      | Section |
   |               |                            | Location,  |  4.2.5, |
   |               |                            | NDay, Offs | Section |
   |               |                            | etTrigger, |  4.4.5, |
   |               |                            | Participan | Section |
   |               |                            | t, Recurre |  4.3.2, |
   |               |                            | nceRule,   | Section |
   |               |                            | Relation,  |  4.1.3, |
   |               |                            | TimeZone,  | Section |
   |               |                            | TimeZoneRu |  4.7.2, |
   |               |                            | le, Virtua | Section |
   |               |                            | lLocation  |  4.7.2, |
   |               |                            |            | Section |
   |               |                            |            |  4.2.6  |
   |               |                            |            |         |
   | acknowledged  | UTCDateTime                | Alert      | Section |
   |               |                            |            |  4.5.2  |
   |               |                            |            |         |
   | action        | String                     | Alert      | Section |
   |               |                            |            |  4.5.2  |
   |               |                            |            |         |
   | alerts        | Id[Alert]                  | JSEvent,   | Section |
   |               |                            | JSTask     |  4.5.2  |
   |               |                            |            |         |
   | aliases       | String[Boolean]            | TimeZone   | Section |
   |               |                            |            |  4.7.2  |
   |               |                            |            |         |



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   | byDay         | NDay[]                     | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | byHour        | UnsignedInt[]              | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | byMinute      | UnsignedInt[]              | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | byMonth       | String[]                   | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | byMonthDay    | Int[]                      | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | bySecond      | UnsignedInt[]              | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | bySetPosition | Int[]                      | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | byWeekNo      | Int[]                      | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | byYearDay     | Int[]                      | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | categories    | String[Boolean]            | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.2.10 |
   |               |                            | JSGroup    |         |
   |               |                            |            |         |
   | cid           | String                     | Link       | Section |
   |               |                            |            |  4.2.7  |
   |               |                            |            |         |
   | color         | String                     | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.2.11 |
   |               |                            | JSGroup    |         |
   |               |                            |            |         |
   | comments      | String[]                   | TimeZoneRu | Section |
   |               |                            | le         |  4.7.2  |
   |               |                            |            |         |
   | contentType   | String                     | Link       | Section |
   |               |                            |            |  4.2.7  |
   |               |                            |            |         |
   | coordinates   | String                     | Location   | Section |
   |               |                            |            |  4.2.5  |
   |               |                            |            |         |
   | count         | UnsignedInt                | Recurrence | Section |



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   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | created       | UTCDateTime                | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.1.5  |
   |               |                            | JSGroup    |         |
   |               |                            |            |         |
   | day           | String                     | NDay       | Section |
   |               |                            |            |  4.3.2  |
   |               |                            |            |         |
   | daylight      | TimeZoneRule               | TimeZone   | Section |
   |               |                            |            |  4.7.2  |
   |               |                            |            |         |
   | delegatedFrom | String[Boolean]            | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | delegatedTo   | String[Boolean]            | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | description   | String                     | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.2.2, |
   |               |                            | Location,  | Section |
   |               |                            | Participan |  4.2.5, |
   |               |                            | t, Virtual | Section |
   |               |                            | Location   |  4.4.5, |
   |               |                            |            | Section |
   |               |                            |            |  4.2.6  |
   |               |                            |            |         |
   | descriptionCo | String                     | JSEvent,   | Section |
   | ntentType     |                            | JSTask     |  4.2.3  |
   |               |                            |            |         |
   | display       | String                     | Link       | Section |
   |               |                            |            |  4.2.7  |
   |               |                            |            |         |
   | due           | LocalDateTime              | JSTask     | Section |
   |               |                            |            |  5.2.1  |
   |               |                            |            |         |
   | duration      | Duration                   | JSEvent    | Section |
   |               |                            |            |  5.1.2  |
   |               |                            |            |         |
   | email         | String                     | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | entries       | (JSTask|JSEvent)[]         | JSGroup    | Section |
   |               |                            |            |  5.3.1  |
   |               |                            |            |         |
   | estimatedDura | Duration                   | JSTask     | Section |
   | tion          |                            |            |  5.2.3  |
   |               |                            |            |         |



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   | excluded      | Boolean                    | JSEvent,   | Section |
   |               |                            | JSTask     |  4.3.5  |
   |               |                            |            |         |
   | excludedRecur | RecurrenceRule[]           | JSEvent,   | Section |
   | renceRules    |                            | JSTask     |  4.3.3  |
   |               |                            |            |         |
   | expectReply   | Boolean                    | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | firstDayOfWee | String                     | Recurrence | Section |
   | k             |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | freeBusyStatu | String                     | JSEvent,   | Section |
   | s             |                            | JSTask     |  4.4.2  |
   |               |                            |            |         |
   | frequency     | String                     | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | href          | String                     | Link       | Section |
   |               |                            |            |  4.2.7  |
   |               |                            |            |         |
   | interval      | UnsignedInt                | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | invitedBy     | String                     | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | keywords      | String[Boolean]            | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.2.9  |
   |               |                            | JSGroup    |         |
   |               |                            |            |         |
   | kind          | String                     | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | language      | String                     | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | linkIds       | Id[Boolean]                | Location,  | Section |
   |               |                            | Participan |  4.2.5, |
   |               |                            | t          | Section |
   |               |                            |            |  4.4.5  |
   |               |                            |            |         |
   | links         | Id[Link]                   | JSGroup,   | Section |
   |               |                            | JSEvent,   |  4.2.7  |
   |               |                            | JSTask     |         |
   |               |                            |            |         |
   | locale        | String                     | JSGroup,   | Section |
   |               |                            | JSEvent,   |  4.2.7  |



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   |               |                            | JSTask     |         |
   |               |                            |            |         |
   | localizations | String[PatchObject]        | JSEvent,   | Section |
   |               |                            | JSTask     |  4.6.1  |
   |               |                            |            |         |
   | locationId    | String                     | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | locations     | Id[Location]               | JSEvent,   | Section |
   |               |                            | JSTask     |  4.2.5  |
   |               |                            |            |         |
   | locationTypes | String[Boolean]            | Location   | Section |
   |               |                            |            |  4.2.5  |
   |               |                            |            |         |
   | memberOf      | String[Boolean]            | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | method        | String                     | JSEvent,   | Section |
   |               |                            | JSTask     |  4.1.8  |
   |               |                            |            |         |
   | name          | String                     | Location,  | Section |
   |               |                            | VirtualLoc |  4.2.5, |
   |               |                            | ation, Par | Section |
   |               |                            | ticipant   |  4.2.6, |
   |               |                            |            | Section |
   |               |                            |            |  4.4.5  |
   |               |                            |            |         |
   | names         | String[Boolean]            | TimeZoneRu | Section |
   |               |                            | le         |  4.7.2  |
   |               |                            |            |         |
   | nthOfPeriod   | Int                        | NDay       | Section |
   |               |                            |            |  4.3.2  |
   |               |                            |            |         |
   | offset        | SignedDuration             | OffsetTrig | Section |
   |               |                            | ger        |  4.5.2  |
   |               |                            |            |         |
   | offsetFrom    | UTCDateTime                | TimeZoneRu | Section |
   |               |                            | le         |  4.7.2  |
   |               |                            |            |         |
   | offsetTo      | UTCDateTime                | TimeZoneRu | Section |
   |               |                            | le         |  4.7.2  |
   |               |                            |            |         |
   | participants  | Id[Participant]            | JSEvent,   | Section |
   |               |                            | JSTask     |  4.4.5  |
   |               |                            |            |         |
   | participation | String                     | Participan | Section |
   | Comment       |                            | t          |  4.4.5  |
   |               |                            |            |         |



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   | participation | String                     | Participan | Section |
   | Status        |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | percentComple | UnsignedInt                | JSTask, Pa | Section |
   | te            |                            | rticipant  |  5.2.4  |
   |               |                            |            |         |
   | priority      | Int                        | JSEvent,   | Section |
   |               |                            | JSTask     |  4.4.1  |
   |               |                            |            |         |
   | privacy       | String                     | JSEvent,   | Section |
   |               |                            | JSTask     |  4.4.3  |
   |               |                            |            |         |
   | prodId        | String                     | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.1.4  |
   |               |                            | JSGroup    |         |
   |               |                            |            |         |
   | progress      | String                     | JSTask, Pa | Section |
   |               |                            | rticipant  |  5.2.5  |
   |               |                            |            |         |
   | progressUpdat | UTCDateTime                | JSTask, Pa | Section |
   | ed            |                            | rticipant  |  5.2.6  |
   |               |                            |            |         |
   | recurrenceId  | LocalDateTime              | JSEvent,   | Section |
   |               |                            | JSTask     |  4.3.1  |
   |               |                            |            |         |
   | recurrenceOve | LocalDateTime[PatchObject] | JSEvent,   | Section |
   | rrides        |                            | JSTask, Ti |  4.3.4, |
   |               |                            | meZoneRule | Section |
   |               |                            |            |  4.7.2  |
   |               |                            |            |         |
   | recurrenceRul | RecurrenceRule[]           | JSEvent,   | Section |
   | es            |                            | JSTask, Ti |  4.3.2, |
   |               |                            | meZoneRule | Section |
   |               |                            |            |  4.7.2  |
   |               |                            |            |         |
   | rel           | String                     | Link       | Section |
   |               |                            |            |  4.2.7  |
   |               |                            |            |         |
   | relatedTo     | String[Relation]           | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.1.3, |
   |               |                            | Alert      | Section |
   |               |                            |            |  4.5.2  |
   |               |                            |            |         |
   | relation      | String[Boolean]            | Relation   | Section |
   |               |                            |            |  1.4.10 |
   |               |                            |            |         |
   | relativeTo    | String                     | OffsetTrig | Section |
   |               |                            | ger,       |  4.5.2, |



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   |               |                            | Location   | Section |
   |               |                            |            |  4.2.5  |
   |               |                            |            |         |
   | replyTo       | String[String]             | JSEvent,   | Section |
   |               |                            | JSTask     |  4.4.4  |
   |               |                            |            |         |
   | roles         | String[Boolean]            | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | rscale        | String                     | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | standard      | TimeZoneRule               | TimeZone   | Section |
   |               |                            |            |  4.7.2  |
   |               |                            |            |         |
   | start         | LocalDateTime              | TimeZoneRu | Section |
   |               |                            | le         |  4.7.2  |
   |               |                            |            |         |
   | scheduleAgent | String                     | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | scheduleForce | Boolean                    | Participan | Section |
   | Send          |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | scheduleSeque | UnsignedInt                | Participan | Section |
   | nce           |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | scheduleStatu | String[]                   | Participan | Section |
   | s             |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | scheduleUpdat | UTCDateTime                | Participan | Section |
   | ed            |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | sendTo        | String[String]             | Participan | Section |
   |               |                            | t          |  4.4.5  |
   |               |                            |            |         |
   | sequence      | UnsignedInt                | JSEvent,   | Section |
   |               |                            | JSTask     |  4.1.7  |
   |               |                            |            |         |
   | showWithoutTi | Boolean                    | JSEvent,   | Section |
   | me            |                            | JSTask     |  4.2.4  |
   |               |                            |            |         |
   | size          | UnsignedInt                | Link       | Section |
   |               |                            |            |  4.2.7  |
   |               |                            |            |         |
   | skip          | String                     | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |



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   | source        | String                     | JSGroup    | Section |
   |               |                            |            |  5.3.2  |
   |               |                            |            |         |
   | start         | LocalDateTime              | JSEvent,   | Section |
   |               |                            | JSTask     |  5.1.1, |
   |               |                            |            | Section |
   |               |                            |            |  5.2.2  |
   |               |                            |            |         |
   | status        | String                     | JSEvent    | Section |
   |               |                            |            |  5.1.3  |
   |               |                            |            |         |
   | timeZone      | String|null                | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.7.1, |
   |               |                            | Location   | Section |
   |               |                            |            |  4.2.5  |
   |               |                            |            |         |
   | timeZones     | String[TimeZone]           | JSEvent,   | Section |
   |               |                            | JSTask     |  4.7.2  |
   |               |                            |            |         |
   | title         | String                     | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.2.1  |
   |               |                            | JSGroup,   |         |
   |               |                            | Link       |         |
   |               |                            |            |         |
   | trigger       | OffsetTrigger|AbsoluteTrig | Alert      | Section |
   |               | ger|UnknownTrigger         |            |  4.5.2  |
   |               |                            |            |         |
   | tzId          | String                     | TimeZone   | Section |
   |               |                            |            |  4.7.2  |
   |               |                            |            |         |
   | uid           | String                     | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.1.2  |
   |               |                            | JSGroup    |         |
   |               |                            |            |         |
   | until         | LocalDateTime              | Recurrence | Section |
   |               |                            | Rule       |  4.3.2  |
   |               |                            |            |         |
   | updated       | UTCDateTime                | JSEvent,   | Section |
   |               |                            | JSTask,    |  4.1.6  |
   |               |                            | JSGroup    |         |
   |               |                            |            |         |
   | uri           | String                     | VirtualLoc | Section |
   |               |                            | ation      |  4.2.6  |
   |               |                            |            |         |
   | url           | String                     | TimeZone   | Section |
   |               |                            |            |  4.7.2  |
   |               |                            |            |         |
   | useDefaultAle | Boolean                    | JSEvent,   | Section |



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   | rts           |                            | JSTask     |  4.5.1  |
   |               |                            |            |         |
   | validUntil    | UTCDateTime                | TimeZone   | Section |
   |               |                            |            |  4.7.2  |
   |               |                            |            |         |
   | virtualLocati | Id[VirtualLocation]        | JSEvent,   | Section |
   | ons           |                            | JSTask     |  4.2.6  |
   |               |                            |            |         |
   | when          | UTCDateTime                | AbsoluteTr | Section |
   |               |                            | igger      |  4.5.2  |
   +---------------+----------------------------+------------+---------+

                                  Table 1

8.3.  Creation of "JSCalendar Types" Registry

   The IANA will create the "JSCalendar Types" registry to avoid name
   collisions and provide a complete reference for all data types used
   for JSCalendar property values.  The registration process is the same
   as for the JSCalendar Properties registry, as defined in Section 8.2.

8.3.1.  JSCalendar Types Registry Template

   o  Type Name: The name of the type.

   o  Reference or Description: A brief description or RFC number and
      section reference where the Type is specified (may be omitted for
      "reserved" type names).

   o  Intended Use: Common, reserved, or obsolete.

   o  Change Controller: ("IETF" for IETF-stream RFCs).

8.3.2.  Initial Contents for the JSCalendar Types Registry

   The following table lists the initial entries of the JSCalendar Types
   registry.  All properties are for common-use.  All RFC section
   references are for this document.  The change controller for all
   these properties is "IETF".












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              +-----------------+--------------------------+
              | Type Name       | Reference or Description |
              +-----------------+--------------------------+
              | Alert           | Section 4.5.2            |
              |                 |                          |
              | Boolean         | Section 1.3              |
              |                 |                          |
              | Duration        | Section 1.4.5            |
              |                 |                          |
              | Id              | Section 1.4.7            |
              |                 |                          |
              | Int             | Section 1.4.1            |
              |                 |                          |
              | LocalDateTime   | Section 1.4.4            |
              |                 |                          |
              | Link            | Section 4.2.7            |
              |                 |                          |
              | Location        | Section 4.2.5            |
              |                 |                          |
              | NDay            | Section 4.3.2            |
              |                 |                          |
              | Number          | Section 1.3              |
              |                 |                          |
              | Participant     | Section 4.4.5            |
              |                 |                          |
              | PatchObject     | Section 1.4.8            |
              |                 |                          |
              | RecurrenceRule  | Section 4.3.2            |
              |                 |                          |
              | Relation        | Section 1.4.10           |
              |                 |                          |
              | SignedDuration  | Section 1.4.6            |
              |                 |                          |
              | String          | Section 1.3              |
              |                 |                          |
              | TimeZone        | Section 4.7.2            |
              |                 |                          |
              | TimeZoneRule    | Section 4.7.2            |
              |                 |                          |
              | UnsignedInt     | Section 1.4.2            |
              |                 |                          |
              | UTCDateTime     | Section 1.4.3            |
              |                 |                          |
              | VirtualLocation | Section 4.2.6            |
              +-----------------+--------------------------+

                                  Table 2




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8.4.  Creation of "JSCalendar Enum Values" Registry

   The IANA will create the "JSCalendar Enum Values" registry to allow
   interoperable extension of semantics for properties with enumerable
   values.  Each such property will have a subregistry of allowed
   values.  The registration process for a new enum value or adding a
   new enumerable property is the same as for the JSCalendar Properties
   registry, as defined in Section 8.2.

8.4.1.  JSCalendar Enum Property Template

   This template is for adding a subregistry for a new enumerable
   property to the JSCalendar Enum registry.

   o  Registry Name: This MUST be of the form "Enum Values for
      {property-name} (Context: {context})" where:

      {property-name} is the name(s) of the property or properties where
      these values may be used.  This MUST be registered in the
      JSCalendar Properties registry.

      {context} is the list of allowed object types where the property
      or properties may appear, as registered in the JSCalendar
      Properties registry.  This disambiguates where there may be two
      distinct properties with the same name in different contexts.

   o  Change Controller: ("IETF" for properties defined in IETF-stream
      RFCs).

   o  Initial Contents: The initial list of defined values for this
      enum, using the template defined in Section 8.4.2.

8.4.2.  JSCalendar Enum Value Template

   This template is for adding a new enum value to a subregistry in the
   JSCalendar Enum registry.

   o  Enum Value: The verbatim value of the enum.

   o  Reference or Description: A brief description or RFC number and
      section reference for the semantics of this value.

8.4.3.  Initial Contents for the JSCalendar Enum Registry

   For each subregistry created in this section, all RFC section
   references are for this document and the change controller is IETF.

   ------------------------------------------------------------



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   Enum Values for action (Context: Alert)

                 +------------+--------------------------+
                 | Enum Value | Reference or Description |
                 +------------+--------------------------+
                 | display    | Section 4.5.2            |
                 |            |                          |
                 | email      | Section 4.5.2            |
                 +------------+--------------------------+

                                  Table 3

   ------------------------------------------------------------

   Enum Values for display (Context: Link)

                 +------------+--------------------------+
                 | Enum Value | Reference or Description |
                 +------------+--------------------------+
                 | badge      | Section 4.2.7            |
                 |            |                          |
                 | graphic    | Section 4.2.7            |
                 |            |                          |
                 | fullsize   | Section 4.2.7            |
                 |            |                          |
                 | thumbnail  | Section 4.2.7            |
                 +------------+--------------------------+

                                  Table 4

   ------------------------------------------------------------

   Enum Values for freeBusyStatus (Context: JSEvent, JSTask)

                 +------------+--------------------------+
                 | Enum Value | Reference or Description |
                 +------------+--------------------------+
                 | free       | Section 4.4.2            |
                 |            |                          |
                 | busy       | Section 4.4.2            |
                 +------------+--------------------------+

                                  Table 5

   ------------------------------------------------------------

   Enum Values for kind (Context: Participant)




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                 +------------+--------------------------+
                 | Enum Value | Reference or Description |
                 +------------+--------------------------+
                 | individual | Section 4.4.5            |
                 |            |                          |
                 | group      | Section 4.4.5            |
                 |            |                          |
                 | resource   | Section 4.4.5            |
                 |            |                          |
                 | location   | Section 4.4.5            |
                 +------------+--------------------------+

                                  Table 6

   ------------------------------------------------------------

   Enum Values for participationStatus (Context: Participant)

                +--------------+--------------------------+
                | Enum Value   | Reference or Description |
                +--------------+--------------------------+
                | needs-action | Section 4.4.5            |
                |              |                          |
                | accepted     | Section 4.4.5            |
                |              |                          |
                | declined     | Section 4.4.5            |
                |              |                          |
                | tenative     | Section 4.4.5            |
                |              |                          |
                | delegated    | Section 4.4.5            |
                +--------------+--------------------------+

                                  Table 7

   ------------------------------------------------------------

   Enum Values for privacy (Context: JSEvent, JSTask)














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                 +------------+--------------------------+
                 | Enum Value | Reference or Description |
                 +------------+--------------------------+
                 | public     | Section 4.4.3            |
                 |            |                          |
                 | private    | Section 4.4.3            |
                 |            |                          |
                 | secret     | Section 4.4.3            |
                 +------------+--------------------------+

                                  Table 8

   ------------------------------------------------------------

   Enum Values for progress (Context: JSTask, Participant)

                +--------------+--------------------------+
                | Enum Value   | Reference or Description |
                +--------------+--------------------------+
                | needs-action | Section 5.2.5            |
                |              |                          |
                | in-process   | Section 5.2.5            |
                |              |                          |
                | completed    | Section 5.2.5            |
                |              |                          |
                | failed       | Section 5.2.5            |
                |              |                          |
                | cancelled    | Section 5.2.5            |
                +--------------+--------------------------+

                                  Table 9

   ------------------------------------------------------------

   Enum Values for relation (Context: Relation)
















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                 +------------+--------------------------+
                 | Enum Value | Reference or Description |
                 +------------+--------------------------+
                 | first      | Section 1.4.10           |
                 |            |                          |
                 | next       | Section 1.4.10           |
                 |            |                          |
                 | child      | Section 1.4.10           |
                 |            |                          |
                 | parent     | Section 1.4.10           |
                 +------------+--------------------------+

                                 Table 10

   ------------------------------------------------------------

   Enum Values for relativeTo (Context: OffsetTrigger, Location)

                 +------------+--------------------------+
                 | Enum Value | Reference or Description |
                 +------------+--------------------------+
                 | start      | Section 4.5.2            |
                 |            |                          |
                 | end        | Section 4.5.2            |
                 +------------+--------------------------+

                                 Table 11

   ------------------------------------------------------------

   Enum Values for roles (Context: Participant)




















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               +---------------+--------------------------+
               | Enum Value    | Reference or Description |
               +---------------+--------------------------+
               | owner         | Section 4.4.5            |
               |               |                          |
               | attendee      | Section 4.4.5            |
               |               |                          |
               | optional      | Section 4.4.5            |
               |               |                          |
               | informational | Section 4.4.5            |
               |               |                          |
               | chair         | Section 4.4.5            |
               |               |                          |
               | contact       | Section 4.4.5            |
               +---------------+--------------------------+

                                 Table 12

   ------------------------------------------------------------

   Enum Values for scheduleAgent (Context: Participant)

                 +------------+--------------------------+
                 | Enum Value | Reference or Description |
                 +------------+--------------------------+
                 | server     | Section 4.4.5            |
                 |            |                          |
                 | client     | Section 4.4.5            |
                 |            |                          |
                 | none       | Section 4.4.5            |
                 +------------+--------------------------+

                                 Table 13

   ------------------------------------------------------------

   Enum Values for status (Context: JSEvent)














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                 +------------+--------------------------+
                 | Enum Value | Reference or Description |
                 +------------+--------------------------+
                 | confirmed  | Section 5.1.3            |
                 |            |                          |
                 | cancelled  | Section 5.1.3            |
                 |            |                          |
                 | tentative  | Section 5.1.3            |
                 +------------+--------------------------+

                                 Table 14

9.  Acknowledgments

   The authors would like to thank the members of CalConnect for their
   valuable contributions.  This specification originated from the work
   of the API technical committee of CalConnect, the Calendaring and
   Scheduling Consortium.

10.  References

10.1.  Normative References

   [CLDR]     "Unicode Common Locale Data Repository",
              <http://cldr.unicode.org/>.

   [COLORS]   "CSS Color Module", <https://www.w3.org/TR/css-color-3/>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2392]  Levinson, E., "Content-ID and Message-ID Uniform Resource
              Locators", RFC 2392, DOI 10.17487/RFC2392, August 1998,
              <https://www.rfc-editor.org/info/rfc2392>.

   [RFC2397]  Masinter, L., "The "data" URL scheme", RFC 2397,
              DOI 10.17487/RFC2397, August 1998,
              <https://www.rfc-editor.org/info/rfc2397>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [RFC4589]  Schulzrinne, H. and H. Tschofenig, "Location Types
              Registry", RFC 4589, DOI 10.17487/RFC4589, July 2006,
              <https://www.rfc-editor.org/info/rfc4589>.



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   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5545]  Desruisseaux, B., Ed., "Internet Calendaring and
              Scheduling Core Object Specification (iCalendar)",
              RFC 5545, DOI 10.17487/RFC5545, September 2009,
              <https://www.rfc-editor.org/info/rfc5545>.

   [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
              September 2009, <https://www.rfc-editor.org/info/rfc5646>.

   [RFC5870]  Mayrhofer, A. and C. Spanring, "A Uniform Resource
              Identifier for Geographic Locations ('geo' URI)",
              RFC 5870, DOI 10.17487/RFC5870, June 2010,
              <https://www.rfc-editor.org/info/rfc5870>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/info/rfc6838>.

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/info/rfc6901>.

   [RFC7493]  Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
              DOI 10.17487/RFC7493, March 2015,
              <https://www.rfc-editor.org/info/rfc7493>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.






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   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8288]  Nottingham, M., "Web Linking", RFC 8288,
              DOI 10.17487/RFC8288, October 2017,
              <https://www.rfc-editor.org/info/rfc8288>.

   [TZDB]     "IANA Time Zone Database",
              <https://www.iana.org/time-zones>.

10.2.  Informative References

   [LINKRELS]
              "IANA Link Relation Types",
              <https://www.iana.org/assignments/link-relations/link-
              relations.xhtml>.

   [LOCATIONTYPES]
              "IANA Location Types Registry",
              <https://www.iana.org/assignments/location-type-registry/
              location-type-registry.xhtml>.

   [MIME]     "IANA Media Types", <https://www.iana.org/assignments/
              media-types/media-types.xhtml>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,
              <https://www.rfc-editor.org/info/rfc4122>.

   [RFC5546]  Daboo, C., Ed., "iCalendar Transport-Independent
              Interoperability Protocol (iTIP)", RFC 5546,
              DOI 10.17487/RFC5546, December 2009,
              <https://www.rfc-editor.org/info/rfc5546>.

   [RFC6047]  Melnikov, A., Ed., "iCalendar Message-Based
              Interoperability Protocol (iMIP)", RFC 6047,
              DOI 10.17487/RFC6047, December 2010,
              <https://www.rfc-editor.org/info/rfc6047>.





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   [RFC6376]  Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
              "DomainKeys Identified Mail (DKIM) Signatures", STD 76,
              RFC 6376, DOI 10.17487/RFC6376, September 2011,
              <https://www.rfc-editor.org/info/rfc6376>.

   [RFC7265]  Kewisch, P., Daboo, C., and M. Douglass, "jCal: The JSON
              Format for iCalendar", RFC 7265, DOI 10.17487/RFC7265, May
              2014, <https://www.rfc-editor.org/info/rfc7265>.

   [RFC7529]  Daboo, C. and G. Yakushev, "Non-Gregorian Recurrence Rules
              in the Internet Calendaring and Scheduling Core Object
              Specification (iCalendar)", RFC 7529,
              DOI 10.17487/RFC7529, May 2015,
              <https://www.rfc-editor.org/info/rfc7529>.

   [RFC7808]  Douglass, M. and C. Daboo, "Time Zone Data Distribution
              Service", RFC 7808, DOI 10.17487/RFC7808, March 2016,
              <https://www.rfc-editor.org/info/rfc7808>.

   [RFC7986]  Daboo, C., "New Properties for iCalendar", RFC 7986,
              DOI 10.17487/RFC7986, October 2016,
              <https://www.rfc-editor.org/info/rfc7986>.

Authors' Addresses

   Neil Jenkins
   Fastmail
   PO Box 234
   Collins St West
   Melbourne  VIC 8007
   Australia

   Email: neilj@fastmailteam.com
   URI:   https://www.fastmail.com


   Robert Stepanek
   Fastmail
   PO Box 234
   Collins St West
   Melbourne  VIC 8007
   Australia

   Email: rsto@fastmailteam.com
   URI:   https://www.fastmail.com






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