Non-Gregorian Recurrence Rules in iCalendar
draft-ietf-calext-rscale-00

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Document Type Active Internet-Draft (calext WG)
Last updated 2014-10-29 (latest revision 2014-10-04)
Replaces draft-daboo-icalendar-rscale
Stream IETF
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Send notices to "Donald E. Eastlake 3rd" <d3e3e3@gmail.com>
Network Working Group                                           C. Daboo
Internet-Draft                                                Apple Inc.
Updates: 5545, 5546, 4791 (if approved)                      G. Yakushev
Intended status: Standards Track                             Google Inc.
Expires: April 7, 2015                                   October 4, 2014

              Non-Gregorian Recurrence Rules in iCalendar
                      draft-ietf-calext-rscale-00

Abstract

   This document defines how non-Gregorian recurrence rules can be
   specified and used in iCalendar data, and with CalDAV servers.

Status of This Memo

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

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   This Internet-Draft will expire on April 7, 2015.

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   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Extended RRULE Property . . . . . . . . . . . . . . . . . . .   5
     4.1.  Handling Leap Months  . . . . . . . . . . . . . . . . . .   6
     4.2.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Registering Calendar Systems  . . . . . . . . . . . . . . . .   9
   6.  Use with iTIP . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Use with CalDAV . . . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  CALDAV:supported-rscale-set Property  . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     11.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Appendix A.  Change History (To be removed by RFC Editor before
                publication) . . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The iCalendar [RFC5545] data format is in widespread use to represent
   calendar data. iCalendar represents dates and times using the
   Gregorian calendar system only.  It does provide a way to use non-
   Gregorian calendar systems via a "CALSCALE" property, however this
   has never been formally used.  However, there is a need to support at
   least non-Gregorian recurrence patterns to cover anniversaries, and
   many local, religious, or civil holidays based on non-Gregorian
   dates.

   There are several disadvantages to using the existing "CALSCALE"
   property in iCalendar for implementing non-Gregorian calendars:

   1.  The "CALSCALE" property exists in the top-level "VCALENDAR"
       objects and thus applies to all components within that object.
       In today's multi-cultural society, that restricts the ability to
       mix events from different calendar systems within the same
       iCalendar object. e.g., it would prevent having both the
       Gregorian New Year and Chinese New Year in the same iCalendar
       object.

   2.  Many countries observe daylight savings time, encoded in
       iCalendar using the "VTIMEZONE" component.  Time zone and
       daylight saving time rules are always specified via Gregorian
       calendar based recurrence rules (e.g., "the 3rd Sunday in

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