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Versions: (RFC 2445) 00 01 02 03 04 05 06 07 08 09 10 RFC 5545

Network Working Group                               B. Desruisseaux, Ed.
Internet-Draft                                                    Oracle
Obsoletes: 2445 (if approved)                              June 22, 2006
Expires: December 24, 2006


     Internet Calendaring and Scheduling Core Object Specification
                              (iCalendar)
                    draft-ietf-calsify-rfc2445bis-01

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

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   This Internet-Draft will expire on December 24, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   There is a clear need to provide and deploy interoperable calendaring
   and scheduling services for the Internet.  Current group scheduling
   and Personal Information Management (PIM) products are being extended
   for use across the Internet, today, in proprietary ways.  This memo
   has been defined to provide the definition of a common format for
   openly exchanging calendaring and scheduling information across the
   Internet.



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   This memo is formatted as a registration for a MIME media type .
   However, the format in this memo is equally applicable for use
   outside of a MIME message content type.

   The proposed media type value is 'text/calendar'.  This string would
   label a media type containing calendaring and scheduling information
   encoded as text characters formatted in a manner outlined below.

   This MIME media type provides a standard content type for capturing
   calendar event, to-do and journal entry information.  It also can be
   used to convey free/busy time information.  The content type is
   suitable as a MIME message entity that can be transferred over MIME
   based email systems, using HTTP or some other Internet transport.  In
   addition, the content type is useful as an object for interactions
   between desktop applications using the operating system clipboard,
   drag/drop or file systems capabilities.

   This memo is based on the earlier work of the vCalendar specification
   for the exchange of personal calendaring and scheduling information.
   In order to avoid confusion with this referenced work, this memo is
   to be known as the iCalendar specification.

   This memo defines the format for specifying iCalendar object methods.
   An iCalendar object method is a set of usage constraints for the
   iCalendar object.  For example, these methods might define scheduling
   messages that request an event be scheduled, reply to an event
   request, send a cancellation notice for an event, modify or replace
   the definition of an event, provide a counter proposal for an
   original event request, delegate an event request to another
   individual, request free or busy time, reply to a free or busy time
   request, or provide similar scheduling messages for a to-do or
   journal entry calendar component.  The iCalendar Transport-indendent
   Interoperability Protocol (iTIP) is one such scheduling protocol.

Editorial Note

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

   A detailed list of changes is available at the following page:
   http://www.geocities.com/bdesruisseaux/calsify/
   draft-ietf-calsify-rfc2445bis-01.html.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   6
   2.  Basic Grammar and Conventions . . . . . . . . . . . . . . . .   6
     2.1.  Formatting Conventions  . . . . . . . . . . . . . . . . .   7
     2.2.  Related Memos . . . . . . . . . . . . . . . . . . . . . .   8
     2.3.  International Considerations  . . . . . . . . . . . . . .   8
   3.  iCalendar Object Specification  . . . . . . . . . . . . . . .   9
     3.1.  Content Lines . . . . . . . . . . . . . . . . . . . . . .   9
       3.1.1.  List and Field Separators . . . . . . . . . . . . . .  11
       3.1.2.  Multiple Values . . . . . . . . . . . . . . . . . . .  12
       3.1.3.  Binary Content  . . . . . . . . . . . . . . . . . . .  12
       3.1.4.  Character Set . . . . . . . . . . . . . . . . . . . .  13
     3.2.  Property Parameters . . . . . . . . . . . . . . . . . . .  13
       3.2.1.  Alternate Text Representation . . . . . . . . . . . .  14
       3.2.2.  Common Name . . . . . . . . . . . . . . . . . . . . .  15
       3.2.3.  Calendar User Type  . . . . . . . . . . . . . . . . .  16
       3.2.4.  Delegators  . . . . . . . . . . . . . . . . . . . . .  16
       3.2.5.  Delegatees  . . . . . . . . . . . . . . . . . . . . .  17
       3.2.6.  Directory Entry Reference . . . . . . . . . . . . . .  17
       3.2.7.  Inline Encoding . . . . . . . . . . . . . . . . . . .  18
       3.2.8.  Format Type . . . . . . . . . . . . . . . . . . . . .  19
       3.2.9.  Free/Busy Time Type . . . . . . . . . . . . . . . . .  19
       3.2.10. Language  . . . . . . . . . . . . . . . . . . . . . .  20
       3.2.11. Group or List Membership  . . . . . . . . . . . . . .  21
       3.2.12. Participation Status  . . . . . . . . . . . . . . . .  21
       3.2.13. Recurrence Identifier Range . . . . . . . . . . . . .  23
       3.2.14. Alarm Trigger Relationship  . . . . . . . . . . . . .  23
       3.2.15. Relationship Type . . . . . . . . . . . . . . . . . .  24
       3.2.16. Participation Role  . . . . . . . . . . . . . . . . .  25
       3.2.17. RSVP Expectation  . . . . . . . . . . . . . . . . . .  25
       3.2.18. Sent By . . . . . . . . . . . . . . . . . . . . . . .  26
       3.2.19. Time Zone Identifier  . . . . . . . . . . . . . . . .  26
       3.2.20. Value Data Types  . . . . . . . . . . . . . . . . . .  28
     3.3.  Property Value Data Types . . . . . . . . . . . . . . . .  29
       3.3.1.  Binary  . . . . . . . . . . . . . . . . . . . . . . .  29
       3.3.2.  Boolean . . . . . . . . . . . . . . . . . . . . . . .  30
       3.3.3.  Calendar User Address . . . . . . . . . . . . . . . .  30
       3.3.4.  Date  . . . . . . . . . . . . . . . . . . . . . . . .  31
       3.3.5.  Date-Time . . . . . . . . . . . . . . . . . . . . . .  31
       3.3.6.  Duration  . . . . . . . . . . . . . . . . . . . . . .  34
       3.3.7.  Float . . . . . . . . . . . . . . . . . . . . . . . .  34
       3.3.8.  Integer . . . . . . . . . . . . . . . . . . . . . . .  35
       3.3.9.  Period of Time  . . . . . . . . . . . . . . . . . . .  35
       3.3.10. Recurrence Rule . . . . . . . . . . . . . . . . . . .  37
       3.3.11. Text  . . . . . . . . . . . . . . . . . . . . . . . .  42
       3.3.12. Time  . . . . . . . . . . . . . . . . . . . . . . . .  43
       3.3.13. URI . . . . . . . . . . . . . . . . . . . . . . . . .  46



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       3.3.14. UTC Offset  . . . . . . . . . . . . . . . . . . . . .  46
     3.4.  iCalendar Object  . . . . . . . . . . . . . . . . . . . .  47
     3.5.  Property  . . . . . . . . . . . . . . . . . . . . . . . .  48
     3.6.  Calendar Components . . . . . . . . . . . . . . . . . . .  48
       3.6.1.  Event Component . . . . . . . . . . . . . . . . . . .  49
       3.6.2.  To-do Component . . . . . . . . . . . . . . . . . . .  52
       3.6.3.  Journal Component . . . . . . . . . . . . . . . . . .  54
       3.6.4.  Free/Busy Component . . . . . . . . . . . . . . . . .  55
       3.6.5.  Time Zone Component . . . . . . . . . . . . . . . . .  58
       3.6.6.  Alarm Component . . . . . . . . . . . . . . . . . . .  66
     3.7.  Calendar Properties . . . . . . . . . . . . . . . . . . .  72
       3.7.1.  Calendar Scale  . . . . . . . . . . . . . . . . . . .  72
       3.7.2.  Method  . . . . . . . . . . . . . . . . . . . . . . .  73
       3.7.3.  Product Identifier  . . . . . . . . . . . . . . . . .  74
       3.7.4.  Version . . . . . . . . . . . . . . . . . . . . . . .  75
     3.8.  Component Properties  . . . . . . . . . . . . . . . . . .  76
       3.8.1.  Descriptive Component Properties  . . . . . . . . . .  76
         3.8.1.1.  Attachment  . . . . . . . . . . . . . . . . . . .  76
         3.8.1.2.  Categories  . . . . . . . . . . . . . . . . . . .  77
         3.8.1.3.  Classification  . . . . . . . . . . . . . . . . .  78
         3.8.1.4.  Comment . . . . . . . . . . . . . . . . . . . . .  79
         3.8.1.5.  Description . . . . . . . . . . . . . . . . . . .  80
         3.8.1.6.  Geographic Position . . . . . . . . . . . . . . .  81
         3.8.1.7.  Location  . . . . . . . . . . . . . . . . . . . .  83
         3.8.1.8.  Percent Complete  . . . . . . . . . . . . . . . .  84
         3.8.1.9.  Priority  . . . . . . . . . . . . . . . . . . . .  85
         3.8.1.10. Resources . . . . . . . . . . . . . . . . . . . .  87
         3.8.1.11. Status  . . . . . . . . . . . . . . . . . . . . .  87
         3.8.1.12. Summary . . . . . . . . . . . . . . . . . . . . .  89
       3.8.2.  Date and Time Component Properties  . . . . . . . . .  90
         3.8.2.1.  Date/Time Completed . . . . . . . . . . . . . . .  90
         3.8.2.2.  Date/Time End . . . . . . . . . . . . . . . . . .  91
         3.8.2.3.  Date/Time Due . . . . . . . . . . . . . . . . . .  92
         3.8.2.4.  Date/Time Start . . . . . . . . . . . . . . . . .  93
         3.8.2.5.  Duration  . . . . . . . . . . . . . . . . . . . .  94
         3.8.2.6.  Free/Busy Time  . . . . . . . . . . . . . . . . .  95
         3.8.2.7.  Time Transparency . . . . . . . . . . . . . . . .  96
       3.8.3.  Time Zone Component Properties  . . . . . . . . . . .  97
         3.8.3.1.  Time Zone Identifier  . . . . . . . . . . . . . .  98
         3.8.3.2.  Time Zone Name  . . . . . . . . . . . . . . . . .  99
         3.8.3.3.  Time Zone Offset From . . . . . . . . . . . . . . 100
         3.8.3.4.  Time Zone Offset To . . . . . . . . . . . . . . . 101
         3.8.3.5.  Time Zone URL . . . . . . . . . . . . . . . . . . 101
       3.8.4.  Relationship Component Properties . . . . . . . . . . 102
         3.8.4.1.  Attendee  . . . . . . . . . . . . . . . . . . . . 102
         3.8.4.2.  Contact . . . . . . . . . . . . . . . . . . . . . 105
         3.8.4.3.  Organizer . . . . . . . . . . . . . . . . . . . . 106
         3.8.4.4.  Recurrence ID . . . . . . . . . . . . . . . . . . 108



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         3.8.4.5.  Related To  . . . . . . . . . . . . . . . . . . . 110
         3.8.4.6.  Uniform Resource Locator  . . . . . . . . . . . . 112
         3.8.4.7.  Unique Identifier . . . . . . . . . . . . . . . . 112
       3.8.5.  Recurrence Component Properties . . . . . . . . . . . 114
         3.8.5.1.  Exception Date/Times  . . . . . . . . . . . . . . 114
         3.8.5.2.  Exception Rule  . . . . . . . . . . . . . . . . . 115
         3.8.5.3.  Recurrence Date/Times . . . . . . . . . . . . . . 117
         3.8.5.4.  Recurrence Rule . . . . . . . . . . . . . . . . . 118
       3.8.6.  Alarm Component Properties  . . . . . . . . . . . . . 127
         3.8.6.1.  Action  . . . . . . . . . . . . . . . . . . . . . 128
         3.8.6.2.  Repeat Count  . . . . . . . . . . . . . . . . . . 128
         3.8.6.3.  Trigger . . . . . . . . . . . . . . . . . . . . . 129
       3.8.7.  Change Management Component Properties  . . . . . . . 131
         3.8.7.1.  Date/Time Created . . . . . . . . . . . . . . . . 132
         3.8.7.2.  Date/Time Stamp . . . . . . . . . . . . . . . . . 132
         3.8.7.3.  Last Modified . . . . . . . . . . . . . . . . . . 133
         3.8.7.4.  Sequence Number . . . . . . . . . . . . . . . . . 134
       3.8.8.  Miscellaneous Component Properties  . . . . . . . . . 136
         3.8.8.1.  Non-standard Properties . . . . . . . . . . . . . 136
         3.8.8.2.  Request Status  . . . . . . . . . . . . . . . . . 137
   4.  iCalendar Object Examples . . . . . . . . . . . . . . . . . . 140
   5.  Recommended Practices . . . . . . . . . . . . . . . . . . . . 144
   6.  Registration of Content Type Elements . . . . . . . . . . . . 145
     6.1.  Registration of New and Modified iCalendar Object
           Methods . . . . . . . . . . . . . . . . . . . . . . . . . 145
     6.2.  Registration of New Properties  . . . . . . . . . . . . . 145
       6.2.1.  Define the property . . . . . . . . . . . . . . . . . 146
       6.2.2.  Post the Property definition  . . . . . . . . . . . . 147
       6.2.3.  Allow a comment period  . . . . . . . . . . . . . . . 147
       6.2.4.  Submit the property for approval  . . . . . . . . . . 147
     6.3.  Property Change Control . . . . . . . . . . . . . . . . . 148
   7.  Internationalization Considerations . . . . . . . . . . . . . 148
   8.  Security Considerations . . . . . . . . . . . . . . . . . . . 148
   9.  IANA Consideration  . . . . . . . . . . . . . . . . . . . . . 149
     9.1.  Media Type Registration Information . . . . . . . . . . . 149
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 152
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . . 152
     11.1. Normative References  . . . . . . . . . . . . . . . . . . 152
     11.2. Informative References  . . . . . . . . . . . . . . . . . 153
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . 155
   Intellectual Property and Copyright Statements  . . . . . . . . . 156










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1.  Introduction

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

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

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

   The memo also includes a formal grammar for the content type based on
   the Internet ABNF defined in [RFC2234].  This ABNF is required for
   the implementation of parsers and to serve as the definitive
   reference when ambiguities or questions arise in interpreting the
   descriptive prose definition of the memo.


2.  Basic Grammar and Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY" and



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   "OPTIONAL" in this document are to be interoperated as described in
   [RFC2119].

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

   The notation used in this memo is the ABNF notation of [RFC2234].
   Readers intending on implementing this format defined in this memo
   should be familiar with this notation in order to properly interpret
   the specifications of this memo.

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

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

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

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

2.1.  Formatting Conventions

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



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   requesting a scheduling calendar component be created or modified,
   "REPLY" refers to the method a recipient of a request uses to update
   their status with the "Organizer" of the calendar component.

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

2.2.  Related Memos

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

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

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

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

2.3.  International Considerations

   In the rest of this document, descriptions of characters are of the
   form "character name (codepoint)", where "codepoint" is from the US-
   ASCII character set.  The "character name" is the authoritative
   description; (codepoint) is a reference to that character in US-ASCII
   or US-ASCII compatible sets (for example the ISO-8859-x family, UTF-
   8, ISO-2022-xx, KOI8-R).  If a non-US-ASCII compatible character set
   is used, appropriate code-point from that character set MUST be
   chosen instead.  Use of non-US-ASCII-compatible character sets is NOT
   recommended.




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3.  iCalendar Object Specification

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

3.1.  Content Lines

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

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

   For example the line:

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

   Can be represented as:

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

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

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

   The content information associated with an iCalendar object is



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

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

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

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

   name               = x-name / iana-token

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

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

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

   param              = param-name "=" param-value
                       *("," param-value)
   ; Each property defines the specific ABNF for the parameters
   ; allowed on the property. Refer to specific properties for
   ; precise parameter ABNF.

   param-name = iana-token / x-token

   param-value        = paramtext / quoted-string

   paramtext  = *SAFE-CHAR

   value      = *VALUE-CHAR

   quoted-string      = DQUOTE *QSAFE-CHAR DQUOTE

   NON-US-ASCII       = %x80-F8
   ; Use restricted by charset parameter
   ; on outer MIME object (UTF-8 preferred)

   QSAFE-CHAR = WSP / %x21 / %x23-7E / NON-US-ASCII



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   ; Any character except CTLs and DQUOTE

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

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

   CR = %x0D
   ; carriage return

   LF = %x0A
   ; line feed

   CRLF       = CR LF
   ; Internet standard newline

   CTL        = %x00-08 / %x0A-1F / %x7F
     ; Controls

   ALPHA      = %x41-5A / %x61-7A   ; A-Z / a-z

   DIGIT      = %x30-39
     ; 0-9

   DQUOTE     = %x22
     ; Quotation Mark

   WSP        = SPACE / HTAB

   SPACE      = %x20

   HTAB       = %x09

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

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

3.1.1.  List and Field Separators

   Some properties and parameters allow a list of values.  Values in a
   list of values MUST be separated by a COMMA character (US-ASCII



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

   Some property values are defined in terms of multiple parts.  These
   structured property values MUST have their value parts separated by a
   SEMICOLON character (US-ASCII decimal 59).

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

   Property parameters with values containing a COLON, a SEMICOLON or a
   COMMA character MUST be placed in quoted text.

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

        ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT:MAILTO:
         jsmith@host.com

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

3.1.2.  Multiple Values

   Some properties defined in the iCalendar object can have multiple
   values.  The general rule for encoding multi-valued items is to
   simply create a new content line for each value, including the
   property name.  However, it should be noted that some properties
   support encoding multiple values in a single property by separating
   the values with a COMMA character (US-ASCII decimal 44).  Individual
   property definitions should be consulted for determining whether a
   specific property allows multiple values and in which of these two
   forms.

3.1.3.  Binary Content

   Binary content information in an iCalendar object SHOULD be
   referenced using a URI within a property value.  That is the binary
   content information SHOULD be placed in an external MIME entity that
   can be referenced by a URI from within the iCalendar object.  In
   applications where this is not feasible, binary content information
   can be included within an iCalendar object, but only after first
   encoding it into text using the "BASE64" encoding method defined in
   [RFC2045].  Inline binary contact SHOULD only be used in applications
   whose special circumstances demand that an iCalendar object be



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   expressed as a single entity.  A property containing inline binary
   content information MUST specify the "ENCODING" property parameter.
   Binary content information placed external to the iCalendar object
   MUST be referenced by a uniform resource identifier (URI).

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


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

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

     ATTACH;FMTTYPE=image/basic;ENCODING=BASE64;VALUE=BINARY:
      MIICajCCAdOgAwIBAgICBEUwDQYJKoZIhvcNAQEEBQAwdzELMAkGA1U
      EBhMCVVMxLDAqBgNVBAoTI05ldHNjYXBlIENvbW11bmljYXRpb25zIE
        <...remainder of "BASE64" encoded binary data...>

3.1.4.  Character Set

   There is not a property parameter to declare the character set used
   in a property value.  The default character set for an iCalendar
   object is UTF-8 as defined in [RFC2279].

   The "charset" Content-Type parameter can be used in MIME transports
   to specify any other IANA registered character set.

3.2.  Property Parameters

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

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

   DESCRIPTION;ALTREP="http://www.wiz.org":The Fall'98 Wild Wizards
     Conference - - Las Vegas, NV, USA




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

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

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

      ianaparam  = iana-token "=" param-value *("," param-value)

      xparam     = x-name "=" param-value *("," param-value)

3.2.1.  Alternate Text Representation

   Parameter Name: ALTREP

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

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

          altrepparam        = "ALTREP" "=" DQUOTE uri DQUOTE





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

   Example:

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

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

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

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

3.2.2.  Common Name

   Parameter Name: CN

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

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

          cnparam    = "CN" "=" param-value

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

   Example:

          ORGANIZER;CN="John Smith":MAILTO:jsmith@host.com





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3.2.3.  Calendar User Type

   Parameter Name: CUTYPE

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

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

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

   Description: This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter identifies the type of
      calendar user specified by the property.  If not specified on a
      property that allows this parameter, the default is INDIVIDUAL.

   Example:

          ATTENDEE;CUTYPE=GROUP:MAILTO:ietf-calsch@imc.org

3.2.4.  Delegators

   Parameter Name: DELEGATED-FROM

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

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

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

   Description: This parameter can be specified on properties with a
      CAL-ADDRESS value type.  This parameter can be specified on a
      property that has a value type of calendar address.  This
      parameter specifies those calendar users that have delegated their
      participation in a group scheduled event or to-do to the calendar



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      user specified by the property.  The value MUST be a MAILTO URI as
      defined in [RFC1738].  The individual calendar address parameter
      values MUST each be specified in a quoted-string.

   Example:

          ATTENDEE;DELEGATED-FROM="MAILTO:jsmith@host.com":MAILTO:
           jdoe@host.com

3.2.5.  Delegatees

   Parameter Name: DELEGATED-TO

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

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

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

   Description: This parameter can be specified on properties with a
      CAL-ADDRESS value type.  This parameter specifies those calendar
      users whom have been delegated participation in a group scheduled
      event or to-do by the calendar user specified by the property.
      The value MUST be a MAILTO URI as defined in [RFC1738].  The
      individual calendar address parameter values MUST each be
      specified in a quoted-string.

   Example:

          ATTENDEE;DELEGATED-TO="MAILTO:jdoe@host.com","MAILTO:jqpublic@
           host.com":MAILTO:jsmith@host.com

3.2.6.  Directory Entry Reference

   Parameter Name: DIR

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

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

          dirparam   = "DIR" "=" DQUOTE uri DQUOTE





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

   Example:

      ORGANIZER;DIR="ldap://host.com:6666/o=eDABC%20Industries,c=3DUS??
       (cn=3DBJim%20Dolittle)":MAILTO:jimdo@host1.com

3.2.7.  Inline Encoding

   Parameter Name: ENCODING

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

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

          encodingparam      = "ENCODING" "="
                               ("8BIT"
             ; "8bit" text encoding is defined in [RFC2045]
                             / "BASE64"
             ; "BASE64" binary encoding format is defined in [RFC2045]
                             / iana-token
             ; Some other IANA registered iCalendar encoding type
                             / x-name)
             ; A non-standard, experimental encoding type

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

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

   Example:

          ATTACH;FMTYPE=IMAGE/JPEG;ENCODING=BASE64;VALUE=BINARY:MIICajC
           CAdOgAwIBAgICBEUwDQYJKoZIhvcNAQEEBQAwdzELMAkGA1UEBhMCVVMxLDA
           qBgNVBAoTI05ldHNjYXBlIENvbW11bmljYXRpb25zIENvcnBvcmF0aW9uMRw
           <...remainder of "BASE64" encoded binary data...>




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3.2.8.  Format Type

   Parameter Name: FMTTYPE

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

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

    fmttypeparam       = "FMTTYPE" "=" iana-token
                                       ; A IANA registered content type
                                    / x-name
                                       ; A non-standard content type

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

   Example:


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

3.2.9.  Free/Busy Time Type

   Parameter Name: FBTYPE

   Purpose: To specify the free or busy time type.

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

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








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   Description: The parameter specifies the free or busy time type.  The
      value FREE indicates that the time interval is free for
      scheduling.  The value BUSY indicates that the time interval is
      busy because one or more events have been scheduled for that
      interval.  The value BUSY-UNAVAILABLE indicates that the time
      interval is busy and that the interval can not be scheduled.  The
      value BUSY-TENTATIVE indicates that the time interval is busy
      because one or more events have been tentatively scheduled for
      that interval.  If not specified on a property that allows this
      parameter, the default is BUSY.

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

          FREEBUSY;FBTYPE=BUSY:19980415T133000Z/19980415T170000Z

3.2.10.  Language

   Parameter Name: LANGUAGE

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

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

    languageparam =    "LANGUAGE" "=" language

    language = <Text identifying a language, as defined in [RFC1766]>

   Description: This parameter can be specified on properties with a
      text value type.  The parameter identifies the language of the
      text in the property or property parameter value.  The value of
      the "language" property parameter is that defined in [RFC1766].

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

   Example:

          SUMMARY;LANGUAGE=us-EN:Company Holiday Party

          LOCATION;LANGUAGE=en:Germany

          LOCATION;LANGUAGE=no:Tyskland

      The following example makes use of the Quoted-Printable encoding



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      in order to represent non-ASCII characters.


          LOCATION;LANGUAGE=3Dda:K=C3=B8benhavn

          LOCATION;LANGUAGE=en:Copenhagen

3.2.11.  Group or List Membership

   Parameter Name: MEMBER

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

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

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

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

   Example:

    ATTENDEE;MEMBER="MAILTO:ietf-calsch@imc.org":MAILTO:jsmith@host.com

    ATTENDEE;MEMBER="MAILTO:projectA@host.com","MAILTO:projectB@host.
     com":MAILTO:janedoe@host.com

3.2.12.  Participation Status

   Parameter Name: PARTSTAT

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

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






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

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

   Description: This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter identifies the
      participation status for the calendar user specified by the
      property value.  The parameter values differ depending on whether
      they are associated with a group scheduled "VEVENT", "VTODO" or
      "VJOURNAL".  The values MUST match one of the values allowed for
      the given calendar component.  If not specified on a property that
      allows this parameter, the default value is NEEDS-ACTION.



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   Example:

          ATTENDEE;PARTSTAT=DECLINED:MAILTO:jsmith@host.com

3.2.13.  Recurrence Identifier Range

   Parameter Name: RANGE

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

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

    rangeparam = "RANGE" "=" ("THISANDPRIOR"
       ; To specify all instances prior to the recurrence identifier
               / "THISANDFUTURE")
       ; To specify the instance specified by the recurrence identifier
       ; and all subsequent recurrence instances

   Description: The parameter can be specified on a property that
      specifies a recurrence identifier.  The parameter specifies the
      effective range of recurrence instances that is specified by the
      property.  The effective range is from the recurrence identified
      specified by the property.  If this parameter is not specified an
      allowed property, then the default range is the single instance
      specified by the recurrence identifier value of the property.  The
      parameter value can be "THISANDPRIOR" to indicate a range defined
      by the recurrence identified value of the property and all prior
      instances.  The parameter value can also be "THISANDFUTURE" to
      indicate a range defined by the recurrence identifier and all
      subsequent instances.

   Example:

          RECURRENCE-ID;RANGE=THISANDPRIOR:19980401T133000Z

3.2.14.  Alarm Trigger Relationship

   Parameter Name: RELATED

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







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

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

   Description: The parameter can be specified on properties that
      specify an alarm trigger with a DURATION value type.  The
      parameter specifies whether the alarm will trigger relative to the
      start or end of the calendar component.  The parameter value START
      will set the alarm to trigger off the start of the calendar
      component; the parameter value END will set the alarm to trigger
      off the end of the calendar component.  If the parameter is not
      specified on an allowable property, then the default is START.

   Example:

          TRIGGER;RELATED=END:PT5M

3.2.15.  Relationship Type

   Parameter Name: RELTYPE

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

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

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

   Description: This parameter can be specified on a property that
      references another related calendar.  The parameter specifies the
      hierarchical relationship type of the calendar component
      referenced by the property.  The parameter value can be PARENT, to
      indicate that the referenced calendar component is a superior of
      calendar component; CHILD to indicate that the referenced calendar
      component is a subordinate of the calendar component; SIBLING to
      indicate that the referenced calendar component is a peer of the
      calendar component.  If this parameter is not specified on an



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      allowable property, the default relationship type is PARENT.

   Example:

      RELATED-TO;RELTYPE=SIBLING:<19960401-080045-4000F192713@host.com>

3.2.16.  Participation Role

   Parameter Name: ROLE

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

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

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

   Description: This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter specifies the participation
      role for the calendar user specified by the property in the group
      schedule calendar component.  If not specified on a property that
      allows this parameter, the default value is REQ-PARTICIPANT.

   Example:

          ATTENDEE;ROLE=CHAIR:MAILTO:mrbig@host.com

3.2.17.  RSVP Expectation

   Parameter Name: RSVP

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





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

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

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

   Example:

          ATTENDEE;RSVP=TRUE:MAILTO:jsmith@host.com

3.2.18.  Sent By

   Parameter Name: SENT-BY

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

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

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

   Description: This parameter can be specified on properties with a
      CAL-ADDRESS value type.  The parameter specifies the calendar user
      that is acting on behalf of the calendar user specified by the
      property.  The parameter value MUST be a MAILTO URI as defined in
      [RFC1738].  The individual calendar address parameter values MUST
      each be specified in a quoted-string.

   Example:

        ORGANIZER;SENT-BY:"MAILTO:sray@host.com":MAILTO:jsmith@host.com

3.2.19.  Time Zone Identifier

   Parameter Name: TZID







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

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

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

          tzidprefix = "/"

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

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

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



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

      The following are examples of this property parameter:

          DTSTART;TZID=US-Eastern:19980119T020000

          DTEND;TZID=US-Eastern:19980119T030000

      The TZID property parameter MUST NOT be applied to DATE-TIME or



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      TIME properties whose time values are specified in UTC.

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

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

3.2.20.  Value Data Types

   Parameter Name: VALUE

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

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

          valuetypeparam = "VALUE" "=" valuetype

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

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






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

3.3.  Property Value Data Types

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

3.3.1.  Binary

   Value Name: BINARY

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

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

        binary     = *(4b-char) [b-end]
        ; A "BASE64" encoded character string, as defined by [RFC2045].

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

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

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

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

    ATTACH;VALUE=BINARY;ENCODING=BASE64:MIICajCCAdOgAwIBAgICBEUwDQY
     JKoZIhvcNAQEEBQAwdzELMAkGA1UEBhMCVVMxLDAqBgNVBAoTI05ldHNjYXBlI
     ENvbW11bmljYXRpb25zIENvcnBvcmF0aW9uMRwwGgYDVQQLExNJbmZv



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       <...remainder of "BASE64" encoded binary data...>

3.3.2.  Boolean

   Value Name: BOOLEAN

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

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

        boolean    = "TRUE" / "FALSE"

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

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

      GIBBERISH:TRUE

3.3.3.  Calendar User Address

   Value Name: CAL-ADDRESS

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

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

        cal-address        = uri

   Description: The value is a URI as defined by [RFC1738] or any other
      IANA registered form for a URI.  When used to address an Internet
      email transport address for a calendar user, the value MUST be a
      MAILTO URI, as defined by [RFC1738].  No additional content value
      encoding (i.e., BACKSLASH character encoding) is defined for this
      value type.

   Example:

        ATTENDEE:MAILTO:jane_doe@host.com






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3.3.4.  Date

   Value Name: DATE

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

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

        date               = date-value

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

   Description: If the property permits, multiple "date" values are
      specified as a COMMA character (US-ASCII decimal 44) separated
      list of values.  The format for the value type is expressed as the
      [ISO.8601.1988] complete representation, basic format for a
      calendar date.  The textual format specifies a four-digit year,
      two-digit month, and two-digit day of the month.  There are no
      separator characters between the year, month and day component
      text.

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

   Example: The following represents July 14, 1997:

        19970714

3.3.5.  Date-Time

   Value Name: DATE-TIME

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

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

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





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

      The "DATE-TIME" data type is used to identify values that contain
      a precise calendar date and time of day.  The format is based on
      the [ISO.8601.1988] complete representation, basic format for a
      calendar date and time of day.  The text format is a concatenation
      of the "date", followed by the LATIN CAPITAL LETTER T character
      (US-ASCII decimal 84) time designator, followed by the "time"
      format.

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

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

              DTSTART:19980119T230000-0800       ;Invalid time format

      FORM #1: DATE WITH LOCAL TIME

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

              DTSTART:19980118T230000

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







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

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

      FORM #2: DATE WITH UTC TIME

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

              DTSTART:19980119T070000Z

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

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

      The date and local time with reference to time zone information is
      identified by the use the TZID property parameter to reference the
      appropriate time zone definition.  TZID is discussed in detail in
      the section on Time Zone.  For example, the following represents 2
      AM in New York on Janurary 19, 1998:

             DTSTART;TZID=US-Eastern:19980119T020000

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

        DTSTART:19970714T133000            ;Local time
        DTSTART:19970714T173000Z           ;UTC time
        DTSTART;TZID=US-Eastern:19970714T133000    ;Local time and time
                           ; zone reference

      A time value MUST ONLY specify 60 seconds when specifying the
      periodic "leap second" in the time value.  For example:

        COMPLETED:19970630T235960Z







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3.3.6.  Duration

   Value Name: DURATION

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

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

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

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

   Description: If the property permits, multiple "duration" values are
      specified by a COMMA character (US-ASCII decimal 44) separated
      list of values.  The format is expressed as the [ISO.8601.1988]
      basic format for the duration of time.  The format can represent
      durations in terms of weeks, days, hours, minutes, and seconds.

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

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

        P15DT5H0M20S

      A duration of 7 weeks would be:

        P7W

3.3.7.  Float

   Value Name: FLOAT

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

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

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



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

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

   Example:

        1000000.0000001
        1.333
        -3.14

3.3.8.  Integer

   Value Name: INTEGER

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

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

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

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

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

   Example:

        1234567890
        -1234567890
        +1234567890
        432109876

3.3.9.  Period of Time

   Value Name: PERIOD







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

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

      period     = period-explicit / period-start

      period-explicit = date-time "/" date-time
      ; [ISO.8601.1988] complete representation basic format for a
      ; period of time consisting of a start and end. The start MUST
      ; be before the end.

      period-start = date-time "/" dur-value
      ; [ISO.8601.1988] complete representation basic format for a
      ; period of time consisting of a start and positive duration
      ; of time.

   Description: If the property permits, multiple "period" values are
      specified by a COMMA character (US-ASCII decimal 44) separated
      list of values.  There are two forms of a period of time.  First,
      a period of time is identified by its start and its end.  This
      format is expressed as the [ISO.8601.1988] complete
      representation, basic format for "DATE-TIME" start of the period,
      followed by a SOLIDUS character (US-ASCII decimal 47), followed by
      the "DATE-TIME" of the end of the period.  The start of the period
      MUST be before the end of the period.  Second, a period of time
      can also be defined by a start and a positive duration of time.
      The format is expressed as the [ISO.8601.1988] complete
      representation, basic format for the "DATE-TIME" start of the
      period, followed by a SOLIDUS character (US-ASCII decimal 47),
      followed by the [ISO.8601.1988] basic format for "DURATION" of the
      period.

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

        19970101T180000Z/19970102T070000Z

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

        19970101T180000Z/PT5H30M

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





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3.3.10.  Recurrence Rule

   Value Name: RECUR

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

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

    recur      = "FREQ"=freq *(

               ; either UNTIL or COUNT may appear in a 'recur',
               ; but UNTIL and COUNT MUST NOT occur in the same 'recur'

               ( ";" "UNTIL" "=" enddate ) /
               ( ";" "COUNT" "=" 1*DIGIT ) /

               ; the rest of these keywords are optional,
               ; but MUST NOT occur more than once

               ( ";" "INTERVAL" "=" 1*DIGIT )          /
               ( ";" "BYSECOND" "=" byseclist )        /
               ( ";" "BYMINUTE" "=" byminlist )        /
               ( ";" "BYHOUR" "=" byhrlist )           /
               ( ";" "BYDAY" "=" bywdaylist )          /
               ( ";" "BYMONTHDAY" "=" bymodaylist )    /
               ( ";" "BYYEARDAY" "=" byyrdaylist )     /
               ( ";" "BYWEEKNO" "=" bywknolist )       /
               ( ";" "BYMONTH" "=" bymolist )          /
               ( ";" "BYSETPOS" "=" bysplist )         /
               ( ";" "WKST" "=" weekday )              /
               ( ";" x-name "=" text )
               )

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

    enddate    = date
    enddate    =/ date-time            ;An UTC value

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

    seconds    = 1DIGIT / 2DIGIT       ;0 to 59

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

    minutes    = 1DIGIT / 2DIGIT       ;0 to 59



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

    hour       = 1DIGIT / 2DIGIT       ;0 to 23

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

    weekdaynum = [([plus] ordwk / minus ordwk)] weekday

    plus       = "+"

    minus      = "-"

    ordwk      = 1DIGIT / 2DIGIT       ;1 to 53

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

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

    monthdaynum = ([plus] ordmoday) / (minus ordmoday)

    ordmoday   = 1DIGIT / 2DIGIT       ;1 to 31

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

    yeardaynum = ([plus] ordyrday) / (minus ordyrday)

    ordyrday   = 1DIGIT / 2DIGIT / 3DIGIT      ;1 to 366

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

    weeknum    = ([plus] ordwk) / (minus ordwk)

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

    monthnum   = 1DIGIT / 2DIGIT       ;1 to 12

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

    setposday  = yeardaynum

   Description: If the property permits, multiple "recur" values are
      specified by a COMMA character (US-ASCII decimal 44) separated
      list of values.  The value type is a structured value consisting
      of a list of one or more recurrence grammar parts.  Each rule part
      is defined by a NAME=VALUE pair.  The rule parts are separated
      from each other by the SEMICOLON character (US-ASCII decimal 59).



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      The rule parts are not ordered in any particular sequence.
      Individual rule parts MUST only be specified once.

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

      The INTERVAL rule part contains a positive integer representing
      how often the recurrence rule repeats.  The default value is "1",
      meaning every second for a SECONDLY rule, or every minute for a
      MINUTELY rule, every hour for an HOURLY rule, every day for a
      DAILY rule, every week for a WEEKLY rule, every month for a
      MONTHLY rule and every year for a YEARLY rule.

      The UNTIL rule part defines a date-time value which bounds the
      recurrence rule in an inclusive manner.  If the value specified by
      UNTIL is synchronized with the specified recurrence, this date or
      date-time becomes the last instance of the recurrence.  If
      specified as a date-time value, then it MUST be specified in an
      UTC time format.  If not present, and the COUNT rule part is also
      not present, the RRULE is considered to repeat forever.

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

      The BYSECOND rule part specifies a COMMA character (US-ASCII
      decimal 44) separated list of seconds within a minute.  Valid
      values are 0 to 59.  The BYMINUTE rule part specifies a COMMA
      character (US-ASCII decimal 44) separated list of minutes within
      an hour.  Valid values are 0 to 59.  The BYHOUR rule part
      specifies a COMMA character (US- ASCII decimal 44) separated list
      of hours of the day.  Valid values are 0 to 23.

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





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      Each BYDAY value can also be preceded by a positive (+n) or
      negative (-n) integer.  If present, this indicates the nth
      occurrence of the specific day within the MONTHLY or YEARLY RRULE.
      For example, within a MONTHLY rule, +1MO (or simply 1MO)
      represents the first Monday within the month, whereas -1MO
      represents the last Monday of the month.  If an integer modifier
      is not present, it means all days of this type within the
      specified frequency.  For example, within a MONTHLY rule, MO
      represents all Mondays within the month.

      The BYMONTHDAY rule part specifies a COMMA character (ASCII
      decimal 44) separated list of days of the month.  Valid values are
      1 to 31 or -31 to -1.  For example, -10 represents the tenth to
      the last day of the month.

      The BYYEARDAY rule part specifies a COMMA character (US-ASCII
      decimal 44) separated list of days of the year.  Valid values are
      1 to 366 or -366 to -1.  For example, -1 represents the last day
      of the year (December 31st) and -306 represents the 306th to the
      last day of the year (March 1st).

      The BYWEEKNO rule part specifies a COMMA character (US-ASCII
      decimal 44) separated list of ordinals specifying weeks of the
      year.  Valid values are 1 to 53 or -53 to -1.  This corresponds to
      weeks according to week numbering as defined in [ISO.8601.1988].
      A week is defined as a seven day period, starting on the day of
      the week defined to be the week start (see WKST).  Week number one
      of the calendar year is the first week which contains at least
      four (4) days in that calendar year.  This rule part is only valid
      for YEARLY rules.  For example, 3 represents the third week of the
      year.



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

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

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



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      The BYSETPOS rule part specifies a COMMA character (US-ASCII
      decimal 44) separated list of values which corresponds to the nth
      occurrence within the set of events specified by the rule.  Valid
      values are 1 to 366 or -366 to -1.  It MUST only be used in
      conjunction with another BYxxx rule part.  For example "the last
      work day of the month" could be represented as:

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

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

      If BYxxx rule part values are found which are beyond the available
      scope (ie, BYMONTHDAY=30 in February), they are simply ignored.

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

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

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

      Here is an example of evaluating multiple BYxxx rule parts.

          DTSTART;TZID=US-Eastern:19970105T083000
          RRULE:FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;
           BYMINUTE=30



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      First, the "INTERVAL=2" would be applied to "FREQ=YEARLY" to
      arrive at "every other year".  Then, "BYMONTH=1" would be applied
      to arrive at "every January, every other year".  Then, "BYDAY=SU"
      would be applied to arrive at "every Sunday in January, every
      other year".  Then, "BYHOUR=8,9" would be applied to arrive at
      "every Sunday in January at 8 AM and 9 AM, every other year".
      Then, "BYMINUTE=30" would be applied to arrive at "every Sunday in
      January at 8:30 AM and 9:30 AM, every other year".  Then, lacking
      information from RRULE, the second is derived from DTSTART, to end
      up in "every Sunday in January at 8:30:00 AM and 9:30:00 AM, every
      other year".  Similarly, if the BYMINUTE, BYHOUR, BYDAY,
      BYMONTHDAY or BYMONTH rule part were missing, the appropriate
      minute, hour, day or month would have been retrieved from the
      "DTSTART" property.

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

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

              FREQ=DAILY;COUNT=10;INTERVAL=2

      There are other examples specified in the "RRULE" specification.

3.3.11.  Text

   Value Name: TEXT

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

   Format Definition: The character sets supported by this revision of
      iCalendar are UTF-8 and US-ASCII thereof.  The applicability to
      other character sets is for future work.  The value type is
      defined by the following notation.

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

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

        TSAFE-CHAR = %x20-21 / %x23-2B / %x2D-39 / %x3C-5B
                     %x5D-7E / NON-US-ASCII
           ; Any character except CTLs not needed by the current
           ; character set, DQUOTE, ";", ":", "\", ","



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         Note: Certain other character sets may require modification of
         the above definitions, but this is beyond the scope of this
         document.

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

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

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

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

   Example: A multiple line value of:

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

      would be represented as:

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

3.3.12.  Time

   Value Name: TIME







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

   Format Definition: The data type is defined by the following
      notation:

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

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

    time-utc   = "Z"

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

      The "TIME" data type is used to identify values that contain a
      time of day.  The format is based on the [ISO.8601.1988] complete
      representation, basic format for a time of day.  The text format
      consists of a two-digit 24-hour of the day (i.e., values 0-23),
      two- digit minute in the hour (i.e., values 0-59), and two-digit
      seconds in the minute (i.e., values 0-60).  The seconds value of
      60 MUST only to be used to account for "leap" seconds.  Fractions
      of a second are not supported by this format.

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

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



              230000-0800        ;Invalid time format

      FORM #1 LOCAL TIME

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







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              230000

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

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

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

      FORM #2: UTC TIME

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



              070000Z

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

      FORM #3: LOCAL TIME AND TIME ZONE REFERENCE

      The local time with reference to time zone information form is
      identified by the use the TZID property parameter to reference the
      appropriate time zone definition.  TZID is discussed in detail in
      the section on Time Zone.




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   Example: The following represents 8:30 AM in New York in Winter, five
      hours behind UTC, in each of the three formats using the "X-
      TIMEOFDAY" non-standard property:

        X-TIMEOFDAY:083000

        X-TIMEOFDAY:133000Z

        X-TIMEOFDAY;TZID=US-Eastern:083000

3.3.13.  URI

   Value Name: URI

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

   Format Definition: The data type is defined by the following
      notation:

        uri        = <As defined by any IETF RFC>

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

      The URI value formats in RFC 1738, RFC 2111 and any other IETF
      registered value format can be specified.

      Any IANA registered URI format can be used.  These include, but
      are not limited to, those defined in RFC 1738 and RFC 2111.

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

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

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

        http://host1.com/my-report.txt

3.3.14.  UTC Offset







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   Value Name: UTC-OFFSET

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

   Format Definition: The data type is defined by the following
      notation:

        utc-offset = time-numzone  ;As defined above in time data type

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

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

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

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

        -0500

        +0100

3.4.  iCalendar Object

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

     icalobject = 1*("BEGIN" ":" "VCALENDAR" CRLF
                  icalbody
                  "END" ":" "VCALENDAR" CRLF)

   The following is a simple example of an iCalendar object:






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     BEGIN:VCALENDAR
     VERSION:2.0
     PRODID:-//hacksw/handcal//NONSGML v1.0//EN
     BEGIN:VEVENT
     DTSTART:19970714T170000Z
     DTEND:19970715T035959Z
     SUMMARY:Bastille Day Party
     END:VEVENT
     END:VCALENDAR

3.5.  Property

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

   The following is an example of a property:

     DTSTART:19960415T133000Z

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

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

3.6.  Calendar Components

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

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











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     icalbody   = calprops component

     calprops   = 2*(

                ; 'prodid' and 'version' are both REQUIRED,
                ; but MUST NOT occur more than once

                prodid /version /

                ; 'calscale' and 'method' are optional,
                ; but MUST NOT occur more than once

                calscale        /
                method          /

                x-prop
                )

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

     iana-comp  = "BEGIN" ":" iana-token CRLF

                  1*contentline

                  "END" ":" iana-token CRLF

     x-comp     = "BEGIN" ":" x-name CRLF

                  1*contentline

                  "END" ":" x-name CRLF

   An iCalendar object MUST include the "PRODID" and "VERSION" calendar
   properties.  In addition, it MUST include at least one calendar
   component.  Special forms of iCalendar objects are possible to
   publish just busy time (i.e., only a "VFREEBUSY" calendar component)
   or time zone (i.e., only a "VTIMEZONE" calendar component)
   information.  In addition, a complex iCalendar object is possible
   that is used to capture a complete snapshot of the contents of a
   calendar (e.g., composite of many different calendar components).
   More commonly, an iCalendar object will consist of just a single
   "VEVENT", "VTODO" or "VJOURNAL" calendar component.

3.6.1.  Event Component






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   Component Name: VEVENT

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

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

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

       eventprop  = *(

                  ; the following are optional,
                  ; but MUST NOT occur more than once

                  class / created / description / dtstart / geo /
                  last-mod / location / organizer / priority /
                  dtstamp / seq / status / summary / transp /
                  uid / url / recurid /

                  ; either 'dtend' or 'duration' may appear in
                  ; a 'eventprop', but 'dtend' and 'duration'
                  ; MUST NOT occur in the same 'eventprop'

                  dtend / duration /

                  ; the following are optional,
                  ; and MAY occur more than once

                  attach / attendee / categories / comment /
                  contact / exdate / exrule / rstatus / related /
                  resources / rdate / rrule / x-prop

                  )

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




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

      The "DTSTART" property for a "VEVENT" specifies the inclusive
      start of the event.  For recurring events, it also specifies the
      very first instance in the recurrence set.  The "DTEND" property
      for a "VEVENT" calendar component specifies the non-inclusive end
      of the event.  For cases where a "VEVENT" calendar component
      specifies a "DTSTART" property with a DATE data type but no
      "DTEND" property, the events non-inclusive end is the end of the
      calendar date specified by the "DTSTART" property.  For cases
      where a "VEVENT" calendar component specifies a "DTSTART" property
      with a DATE-TIME data type but no "DTEND" property, the event ends
      on the same calendar date and time of day specified by the
      "DTSTART" property.

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

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

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

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







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

      The following is an example of the "VEVENT" calendar component
      used to represent an anniversary that will occur annually.  Since
      it takes up no time, it will not appear as opaque in a search for
      busy time; no matter what the value of the "TRANSP" property
      indicates:

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

3.6.2.  To-do Component

   Component Name: VTODO

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

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















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

       todoprop   = *(

                  ; the following are optional,
                  ; but MUST NOT occur more than once

                  class / completed / created / description / dtstamp /
                  dtstart / geo / last-mod / location / organizer /
                  percent / priority / recurid / seq / status /
                  summary / uid / url /

                  ; either 'due' or 'duration' may appear in
                  ; a 'todoprop', but 'due' and 'duration'
                  ; MUST NOT occur in the same 'todoprop'

                  due / duration /

                  ; the following are optional,
                  ; and MAY occur more than once
                  attach / attendee / categories / comment / contact /
                  exdate / exrule / rstatus / related / resources /
                  rdate / rrule / x-prop

                  )

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

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

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

   Example: The following is an example of a "VTODO" calendar component:







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       BEGIN:VTODO
       UID:19970901T130000Z-123404@host.com
       DTSTAMP:19970901T130000Z
       DTSTART:19970415T133000Z
       DUE:19970416T045959Z
       SUMMARY:1996 Income Tax Preparation
       CLASS:CONFIDENTIAL
       CATEGORIES:FAMILY,FINANCE
       PRIORITY:1
       STATUS:NEEDS-ACTION
       END:VTODO

3.6.3.  Journal Component

   Component Name: VJOURNAL

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

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

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

       jourprop   = *(

                  ; the following are optional,
                  ; but MUST NOT occur more than once

                  class / created / description / dtstart / dtstamp /
                  last-mod / organizer / recurid / seq / status /
                  summary / uid / url /

                  ; the following are optional,
                  ; and MAY occur more than once

                  attach / attendee / categories / comment /
                  contact / exdate / exrule / related / rdate /
                  rrule / rstatus / x-prop
                  )

   Description: A "VJOURNAL" calendar component is a grouping of
      component properties that represent one or more descriptive text
      notes associated with a particular calendar date.  The "DTSTART"
      property is used to specify the calendar date that the journal
      entry is associated with.  Generally, it will have a DATE value



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      data type, but it can also be used to specify a DATE-TIME value
      data type.  Examples of a journal entry include a daily record of
      a legislative body or a journal entry of individual telephone
      contacts for the day or an ordered list of accomplishments for the
      day.  The "VJOURNAL" calendar component can also be used to
      associate a document with a calendar date.

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

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

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

       BEGIN:VJOURNAL
       UID:19970901T130000Z-123405@host.com
       DTSTAMP:19970901T130000Z
       DTSTART;VALUE=DATE:19970317
       SUMMARY:Staff meeting minutes
       DESCRIPTION:1. Staff meeting: Participants include Joe\, Lisa
         and Bob. Aurora project plans were reviewed. There is currently
         no budget reserves for this project. Lisa will escalate to
         management. Next meeting on Tuesday.\n
         2. Telephone Conference: ABC Corp. sales representative called
         to discuss new printer. Promised to get us a demo by Friday.\n
         3. Henry Miller (Handsoff Insurance): Car was totaled by tree.
         Is looking into a loaner car. 654-2323 (tel).
       END:VJOURNAL

3.6.4.  Free/Busy Component

   Component Name: VFREEBUSY

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

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





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

       fbprop     = *(

                  ; the following are optional,
                  ; but MUST NOT occur more than once

                  contact / dtstart / dtend / duration / dtstamp /
                  organizer / uid / url /

                  ; the following are optional,
                  ; and MAY occur more than once

                  attendee / comment / freebusy / rstatus / x-prop
                  )

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

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

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

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




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

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

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

      When present in a "VFREEBUSY" calendar component, the "DTSTART"
      and "DTEND" properties SHOULD be specified prior to any "FREEBUSY"
      properties.  In a free time request, these properties can be used
      in combination with the "DURATION" property to represent a request
      for a duration of free time within a specified window of time.

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

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

       BEGIN:VFREEBUSY
       ORGANIZER:MAILTO:jane_doe@host1.com
       ATTENDEE:MAILTO:john_public@host2.com
       DTSTART:19971015T050000Z
       DTEND:19971016T050000Z
       DTSTAMP:19970901T083000Z
       END:VFREEBUSY

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











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       BEGIN:VFREEBUSY
       ORGANIZER:MAILTO:jane_doe@host1.com
       ATTENDEE:MAILTO:john_public@host2.com
       DTSTAMP:19970901T100000Z
       FREEBUSY;VALUE=PERIOD:19971015T050000Z/PT8H30M,
        19971015T160000Z/PT5H30M,19971015T223000Z/PT6H30M
       URL:http://host2.com/pub/busy/jpublic-01.ifb
       COMMENT:This iCalendar file contains busy time information for
         the next three months.
       END:VFREEBUSY

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

       BEGIN:VFREEBUSY
       ORGANIZER:jsmith@host.com
       DTSTART:19980313T141711Z
       DTEND:19980410T141711Z
       FREEBUSY:19980314T233000Z/19980315T003000Z
       FREEBUSY:19980316T153000Z/19980316T163000Z
       FREEBUSY:19980318T030000Z/19980318T040000Z
       URL:http://www.host.com/calendar/busytime/jsmith.ifb
       END:VFREEBUSY

3.6.5.  Time Zone Component

   Component Name: VTIMEZONE

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

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

       timezonec  = "BEGIN" ":" "VTIMEZONE" CRLF

                    2*(

                    ; 'tzid' is required, but MUST NOT occur more
                    ; than once

                  tzid /

                    ; 'last-mod' and 'tzurl' are optional,
                  but MUST NOT occur more than once

                  last-mod / tzurl /




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                    ; one of 'standardc' or 'daylightc' MUST occur
                    ; and each MAY occur more than once.

                  standardc / daylightc /

                  ; the following is optional,
                  ; and MAY occur more than once

                    x-prop

                    )

                    "END" ":" "VTIMEZONE" CRLF

       standardc  = "BEGIN" ":" "STANDARD" CRLF

                    tzprop

                    "END" ":" "STANDARD" CRLF

       daylightc  = "BEGIN" ":" "DAYLIGHT" CRLF

                    tzprop

                    "END" ":" "DAYLIGHT" CRLF

       tzprop     = 3*(

                  ; the following are each REQUIRED,
                  ; but MUST NOT occur more than once

                  dtstart / tzoffsetto / tzoffsetfrom /

                  ; the following are optional,
                  ; and MAY occur more than once

                  comment / rdate / rrule / tzname / x-prop

                  )

   Description: A time zone is unambiguously defined by the set of time
      measurement rules determined by the governing body for a given
      geographic area.  These rules describe at a minimum the base
      offset from UTC for the time zone, often referred to as the
      Standard Time offset.  Many locations adjust their Standard Time
      forward or backward by one hour, in order to accommodate seasonal
      changes in number of daylight hours, often referred to as Daylight
      Saving Time.  Some locations adjust their time by a fraction of an



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      hour.  Standard Time is also known as Winter Time.  Daylight
      Saving Time is also known as Advanced Time, Summer Time, or Legal
      Time in certain countries.  The following table shows the changes
      in time zone rules in effect for New York City starting from 1967.
      Each line represents a description or rule for a particular
      observance.

                         Effective Observance Rule

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



       Effective Observance Rule

       Date       (Date/Time)             Offset  Abbreviation

       1967-*     last Sun in Oct, 02:00  -0500   EST

       1967-1973  last Sun in Apr, 02:00  -0400   EDT

       1974-1974  Jan 6,  02:00           -0400   EDT

       1975-1975  Feb 23, 02:00           -0400   EDT

       1976-1986  last Sun in Apr, 02:00  -0400   EDT

       1987-*     first Sun in Apr, 02:00 -0400   EDT



         Note: The specification of a global time zone registry is not
         addressed by this document and is left for future study.
         However, implementers may find the Olson time zone database
         [TZDB] a useful reference.  It is an informal, public-domain
         collection of time zone information, which is currently being
         maintained by volunteer Internet participants, and is used in
         several operating systems.  This database contains current and
         historical time zone information for a wide variety of



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         locations around the globe; it provides a time zone identifier
         for every unique time zone rule set in actual use since 1970,
         with historical data going back to the introduction of standard
         time.

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

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

      The "VTIMEZONE" calendar component MUST be present if the
      iCalendar object contains an RRULE that generates dates on both
      sides of a time zone shift (e.g., both in Standard Time and
      Daylight Saving Time) unless the iCalendar object intends to
      convey a floating time ( see Section 3.3.12 for proper
      interpretation of floating time).  It can be present if the
      iCalendar object does not contain such a RRULE.  In addition, if a
      RRULE is present, there MUST be valid time zone information for
      all recurrence instances.

      The "VTIMEZONE" calendar component MUST include the "TZID"
      property and at least one definition of a standard or daylight
      component.  The standard or daylight component MUST include the
      "DTSTART", "TZOFFSETFROM" and "TZOFFSETTO" properties.

      An individual "VTIMEZONE" calendar component MUST be specified for
      each unique "TZID" parameter value specified in the iCalendar
      object.

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



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         the first onset date-time for the observance

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

         the offset to be applied for the observance

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

         an optional name for the observance

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

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

      The mandatory "TZID" property is a text value that uniquely
      identifies the VTIMEZONE; and each MAY occur more than once.
      calendar component within the scope of an iCalendar object.

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

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

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

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







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

       DTSTART:19671029T020000

       TZOFFSETFROM:-0400

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

      The optional "TZNAME" property is the customary name for the time
      zone.  It may be specified multiple times, to allow for specifying
      multiple language variants of the time zone names.  This could be
      used for displaying dates.

      If specified, the onset for the observance defined by the time
      zone sub-component is defined by either the "RRULE" or "RDATE"
      property.  If neither is specified, only one sub-component can be
      specified in the "VTIMEZONE" calendar component and it is assumed
      that the single observance specified is always in effect.

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

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

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

      Alternatively, the "RDATE" property can be used to define the
      onset of the observance by giving the individual onset date and
      times.  "RDATE" in this usage MUST be specified as a local DATE-
      TIME value in UTC time.






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

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

      This is an example showing time zone information for the Eastern
      United States using "RDATE" property.  Note that this is only
      suitable for a recurring event that starts on or later than April
      6, 1997 at 03:00:00 EDT (i.e., the earliest effective transition
      date and time) and ends no later than April 7, 1998 02:00:00 EST
      (i.e., latest valid date and time for EST in this scenario).  For
      example, this can be used for a recurring event that occurs every
      Friday, 8:00AM-9:00 AM, starting June 1, 1997, ending December 31,
      1997.

       BEGIN:VTIMEZONE
       TZID:US-Eastern
       LAST-MODIFIED:19870101T000000Z
       BEGIN:STANDARD
       DTSTART:19971026T020000
       RDATE:19971026T020000
       TZOFFSETFROM:-0400
       TZOFFSETTO:-0500
       TZNAME:EST
       END:STANDARD
       BEGIN:DAYLIGHT
       DTSTART:19970406T020000
       RDATE:19970406T020000
       TZOFFSETFROM:-0500
       TZOFFSETTO:-0400
       TZNAME:EDT
       END:DAYLIGHT
       END:VTIMEZONE

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











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       BEGIN:VTIMEZONE
       TZID:US-Eastern
       LAST-MODIFIED:19870101T000000Z
       TZURL:http://zones.example.com/tz/US-Eastern.ics
       BEGIN:STANDARD
       DTSTART:19671029T020000
       RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
       TZOFFSETFROM:-0400
       TZOFFSETTO:-0500
       TZNAME:EST
       END:STANDARD
       BEGIN:DAYLIGHT
       DTSTART:19870405T020000
       RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
       TZOFFSETFROM:-0500
       TZOFFSETTO:-0400
       TZNAME:EDT
       END:DAYLIGHT
       END:VTIMEZONE

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

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








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

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

3.6.6.  Alarm Component

   Component Name: VALARM

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

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

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

       audioprop  = 2*(

                  ; 'action' and 'trigger' are both REQUIRED,



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                  ; but MUST NOT occur more than once

                  action / trigger /

                  ; 'duration' and 'repeat' are both optional,
                  ; and MUST NOT occur more than once each,
                  ; but if one occurs, so MUST the other

                  duration / repeat /

                  ; the following is optional,
                  ; but MUST NOT occur more than once

                  attach /

                  ; the following is optional,
                  ; and MAY occur more than once

                  x-prop

                  )

       dispprop   = 3*(

                  ; the following are all REQUIRED,
                  ; but MUST NOT occur more than once

                  action / description / trigger /

                  ; 'duration' and 'repeat' are both optional,
                  ; and MUST NOT occur more than once each,
                  ; but if one occurs, so MUST the other

                  duration / repeat /

                  ; the following is optional,
                  ; and MAY occur more than once

                  x-prop

                  )

       emailprop  = 5*(

                  ; the following are all REQUIRED,
                  ; but MUST NOT occur more than once

                  action / description / trigger / summary /



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                  ; the following is REQUIRED,
                  ; and MAY occur more than once

                  attendee /

                  ; 'duration' and 'repeat' are both optional,
                  ; and MUST NOT occur more than once each,
                  ; but if one occurs, so MUST the other

                  duration / repeat /

                  ; the following are optional,
                  ; and MAY occur more than once

                  attach / x-prop

                  )

       procprop   = 3*(

                  ; the following are all REQUIRED,
                  ; but MUST NOT occur more than once

                  action / attach / trigger /

                  ; 'duration' and 'repeat' are both optional,
                  ; and MUST NOT occur more than once each,
                  ; but if one occurs, so MUST the other

                  duration / repeat /

                  ; 'description' is optional,
                  ; and MUST NOT occur more than once

                  description /

                  ; the following is optional,
                  ; and MAY occur more than once

                  x-prop

                  )

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




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

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

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

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

      When the action is "PROCEDURE", the alarm MUST include one and
      only one "ATTACH" property, which MUST point to a procedure
      resource, which is invoked when the alarm is triggered.

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

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

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



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

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

      In an AUDIO alarm, if the optional "ATTACH" property is included,
      it MUST specify an audio sound resource.  The intention is that
      the sound will be played as the alarm effect.  If an "ATTACH"
      property is specified that does not refer to a sound resource, or
      if the specified sound resource cannot be rendered (because its
      format is unsupported, or because it cannot be retrieved), then
      the CUA or other entity responsible for playing the sound may
      choose a fallback action, such as playing a built-in default
      sound, or playing no sound at all.

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

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





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      In a PROCEDURE alarm, the "ATTACH" property in the "VALARM"
      calendar component MUST specify a procedure or program that is
      intended to be invoked as the alarm effect.  If the procedure or
      program is in a format that cannot be rendered, then no procedure
      alarm will be invoked.  If the "DESCRIPTION" property is present,
      its value specifies the argument string to be passed to the
      procedure or program.  "Calendar User Agents" that receive an
      iCalendar object with this category of alarm, can disable or allow
      the "Calendar User" to disable, or otherwise ignore this type of
      alarm.  While a very useful alarm capability, the PROCEDURE type
      of alarm SHOULD be treated by the "Calendar User Agent" as a
      potential security risk.

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

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

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

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

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







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

      The following example is for a "VALARM" calendar component that
      specifies a procedural alarm that will trigger at a precise date/
      time and will repeat 23 more times at one hour intervals.  The
      alarm will invoke a procedure file.

       BEGIN:VALARM
       TRIGGER;VALUE=DATE-TIME:19980101T050000Z
       REPEAT:23
       DURATION:PT1H
       ACTION:PROCEDURE
       ATTACH;FMTTYPE=application/octet-stream:ftp://host.com/novo-
        procs/felizano.exe
       END:VALARM

3.7.  Calendar Properties

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

3.7.1.  Calendar Scale

   Property Name: CALSCALE

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

   Value Type: TEXT

   Property Parameters: Non-standard property parameters can be
      specified on this property.







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

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

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

         calscale   = "CALSCALE" calparam ":" calvalue CRLF

         calparam   = *(";" xparam)

         calvalue   = "GREGORIAN" / iana-token

   Example: The following is an example of this property:

         CALSCALE:GREGORIAN

3.7.2.  Method

   Property Name: METHOD

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

   Value Type: TEXT

   Property Parameters: Non-standard property parameters can be
      specified on this property.

   Conformance: The property can be specified in an iCalendar object.

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

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





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

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

         method     = "METHOD" metparam ":" metvalue CRLF

         metparam   = *(";" xparam)

         metvalue   = iana-token

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

         METHOD:REQUEST

3.7.3.  Product Identifier

   Property Name: PRODID

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

   Value Type: TEXT

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

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

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

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







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         prodid     = "PRODID" pidparam ":" pidvalue CRLF

         pidparam   = *(";" xparam)

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

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

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

3.7.4.  Version

   Property Name: VERSION

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

   Value Type: TEXT

   Property Parameters: Non-standard property parameters can be
      specified on this property.

   Conformance: This property MUST be specified by an iCalendar object,
      but MUST only be specified once.

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

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

         version    = "VERSION" verparam ":" vervalue CRLF

         verparam   = *(";" xparam)

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

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

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




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   Example: The following is an example of this property:

         VERSION:2.0

3.8.  Component Properties

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

3.8.1.  Descriptive Component Properties

   The following properties specify descriptive information about
   calendar components.

3.8.1.1.  Attachment

   Property Name: ATTACH

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

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

   Property Parameters: Non-standard, inline encoding, format type and
      value data type property parameters can be specified on this
      property.

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

   Description: The property can be specified within "VEVENT", "VTODO",
      "VJOURNAL", or "VALARM" calendar components.  This property can be
      specified multiple times within an iCalendar object.

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














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         attach     = "ATTACH" attparam ":" uri  CRLF

         attach     =/ "ATTACH" attparam ";" "ENCODING" "=" "BASE64"
                       ";" "VALUE" "=" "BINARY" ":" binary

         attparam   = *(

                    ; the following is optional,
                    ; but MUST NOT occur more than once

                    (";" fmttypeparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

   Example: The following are examples of this property:

         ATTACH:CID:jsmith.part3.960817T083000.xyzMail@host1.com

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

3.8.1.2.  Categories

   Property Name: CATEGORIES

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

   Value Type: TEXT

   Property Parameters: Non-standard and language property parameters
      can be specified on this property.

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

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




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

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

         catparam   = *(

                    ; the following is optional,
                    ; but MUST NOT occur more than once

                    (";" languageparam ) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

   Example: The following are examples of this property:

         CATEGORIES:APPOINTMENT,EDUCATION

         CATEGORIES:MEETING

3.8.1.3.  Classification

   Property Name: CLASS

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

   Value Type: TEXT

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

   Description: An access classification is only one component of the
      general security system within a calendar application.  It
      provides a method of capturing the scope of the access the
      calendar owner intends for information within an individual
      calendar entry.  The access classification of an individual
      iCalendar component is useful when measured along with the other
      security components of a calendar system (e.g., calendar user
      authentication, authorization, access rights, access role, etc.).



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      Hence, the semantics of the individual access classifications
      cannot be completely defined by this memo alone.  Additionally,
      due to the "blind" nature of most exchange processes using this
      memo, these access classifications cannot serve as an enforcement
      statement for a system receiving an iCalendar object.  Rather,
      they provide a method for capturing the intention of the calendar
      owner for the access to the calendar component.

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

         class      = "CLASS" classparam ":" classvalue CRLF

         classparam = *(";" xparam)

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

   Example: The following is an example of this property:

         CLASS:PUBLIC

3.8.1.4.  Comment

   Property Name: COMMENT

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

   Value Type: TEXT

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

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

   Description: The property can be specified multiple times.

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











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         comment    = "COMMENT" commparam ":" text CRLF

         commparam  = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" altrepparam) / (";" languageparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

   Example: The following is an example of this property:

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

3.8.1.5.  Description

   Property Name: DESCRIPTION

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

   Value Type: TEXT

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

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

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

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






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

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

         description        = "DESCRIPTION" descparam ":" text CRLF

         descparam  = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" altrepparam) / (";" languageparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

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

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

      The following is an example of the property with folding of long
      lines:

         DESCRIPTION:Last draft of the new novel is to be completed
           for the editor's proof today.

3.8.1.6.  Geographic Position

   Property Name: GEO

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

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






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   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

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

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

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

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

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






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

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

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

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

         geo        = "GEO" geoparam ":" geovalue CRLF

         geoparam   = *(";" xparam)

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

   Example: The following is an example of this property:

         GEO:37.386013;-122.082932

3.8.1.7.  Location

   Property Name: LOCATION

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

   Value Type: TEXT

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

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

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




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

         location   = "LOCATION locparam ":" text CRLF

         locparam   = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" altrepparam) / (";" languageparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

   Example: The following are some examples of this property:

         LOCATION:Conference Room - F123, Bldg. 002

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

3.8.1.8.  Percent Complete

   Property Name: PERCENT-COMPLETE

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

   Value Type: INTEGER

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

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






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

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

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

         pctparam   = *(";" xparam)

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

         PERCENT-COMPLETE:39

3.8.1.9.  Priority

   Property Name: PRIORITY

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

   Value Type: INTEGER

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

   Description: The priority is specified as an integer in the range
      zero to nine.  A value of zero (US-ASCII decimal 48) specifies an
      undefined priority.  A value of one (US-ASCII decimal 49) is the
      highest priority.  A value of two (US-ASCII decimal 50) is the
      second highest priority.  Subsequent numbers specify a decreasing
      ordinal priority.  A value of nine (US-ASCII decimal 58) is the
      lowest priority.

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



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      six (US- ASCII decimal 54) to nine (US-ASCII decimal 58) is "LOW"
      priority.

      A CUA with a priority schema of "A1", "A2", "A3", "B1", "B2", ...,
      "C3" is mapped into this property such that a property value of
      one (US-ASCII decimal 49) specifies "A1", a property value of two
      (US- ASCII decimal 50) specifies "A2", a property value of three
      (US-ASCII decimal 51) specifies "A3", and so forth up to a
      property value of 9 (US-ASCII decimal 58) specifies "C3".

      Other integer values are reserved for future use.

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

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

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

         priority   = "PRIORITY" prioparam ":" privalue CRLF
         ;Default is zero

         prioparam  = *(";" xparam)

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

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

         PRIORITY:1

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

         PRIORITY:2

   Example: The following is an example of a property with no priority.

      This is equivalent to not specifying the "PRIORITY" property:

         PRIORITY:0






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3.8.1.10.  Resources

   Property Name: RESOURCES

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

   Value Type: TEXT

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

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

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

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

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

         resrcparam = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" altrepparam) / (";" languageparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

   Example: The following is an example of this property:

         RESOURCES:EASEL,PROJECTOR,VCR

         RESOURCES;LANGUAGE=fr:1 raton-laveur

3.8.1.11.  Status







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   Property Name: STATUS

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

   Value Type: TEXT

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

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

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

     status     = "STATUS" statparam] ":" statvalue CRLF

     statparam  = *(";" xparam)

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

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

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



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

         STATUS:TENTATIVE

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

         STATUS:NEEDS-ACTION

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

         STATUS:DRAFT

3.8.1.12.  Summary

   Property Name: SUMMARY

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

   Value Type: TEXT

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

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

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

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

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













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         summary    = "SUMMARY" summparam ":" text CRLF

         summparam  = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" altrepparam) / (";" languageparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

   Example: The following is an example of this property:

         SUMMARY:Department Party

3.8.2.  Date and Time Component Properties

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

3.8.2.1.  Date/Time Completed

   Property Name: COMPLETED

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

   Value Type: DATE-TIME

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

   Description: The date and time MUST be in a UTC format.

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

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

         compparam  = *(";" xparam)




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   Example: The following is an example of this property:

         COMPLETED:19960401T235959Z

3.8.2.2.  Date/Time End

   Property Name: DTEND

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

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

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

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

   Description: Within the "VEVENT" calendar component, this property
      defines the date and time by which the event ends.  The value MUST
      be later in time than the value of the "DTSTART" property.

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

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





















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         dtend      = "DTEND" dtendparam":" dtendval CRLF

         dtendparam = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                    (";" tzidparam) /

                    ; the following is optional,
                    ; and MAY occur more than once


                    (";" xparam)

                    )

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

   Example: The following is an example of this property:

         DTEND:19960401T235959Z

         DTEND;VALUE=DATE:19980704

3.8.2.3.  Date/Time Due

   Property Name: DUE

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

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

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

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

   Description: The value MUST be a date/time equal to or after the
      DTSTART value, if specified.






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

         due        = "DUE" dueparam":" dueval CRLF

         dueparam   = *(
                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                    (";" tzidparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    *(";" xparam)

                    )

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

   Example: The following is an example of this property:

         DUE:19980430T235959Z

3.8.2.4.  Date/Time Start

   Property Name: DTSTART

   Purpose: This property specifies when the calendar component begins.

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

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

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

   Description: Within the "VEVENT" calendar component, this property
      defines the start date and time for the event.  The property is
      REQUIRED in "VEVENT" calendar components.  Events can have a start
      date/time but no end date/time.  In that case, the event does not
      take up any time.





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

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

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

         dtstart    = "DTSTART" dtstparam ":" dtstval CRLF

         dtstparam  = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /
                    (";" tzidparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                      *(";" xparam)

                    )

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

   Example: The following is an example of this property:

         DTSTART:19980118T073000Z

3.8.2.5.  Duration

   Property Name: DURATION

   Purpose: The property specifies a positive duration of time.

   Value Type: DURATION

   Property Parameters: Non-standard property parameters can be
      specified on this property.





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

   Description: In a "VEVENT" calendar component the property may be
      used to specify a duration of the event, instead of an explicit
      end date/time.  In a "VTODO" calendar component the property may
      be used to specify a duration for the to-do, instead of an
      explicit due date/time.  In a "VFREEBUSY" calendar component the
      property may be used to specify the interval of free time being
      requested.  In a "VALARM" calendar component the property may be
      used to specify the delay period prior to repeating an alarm.

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

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

         durparam   = *(";" xparam)

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

         DURATION:PT1H0M0S

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

         DURATION:PT15M

3.8.2.6.  Free/Busy Time

   Property Name: FREEBUSY

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

   Value Type: PERIOD.  The date and time values MUST be in an UTC time
      format.

   Property Parameters: Non-standard or free/busy time type property
      parameters can be specified on this property.

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







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

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

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

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

         freebusy   = "FREEBUSY" fbparam ":" fbvalue
                      CRLF

         fbparam    = *(
                    ; the following is optional,
                    ; but MUST NOT occur more than once

                    (";" fbtypeparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

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

   Example: The following are some examples of this property:

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

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

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

3.8.2.7.  Time Transparency






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   Property Name: TRANSP

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

   Value Type: TEXT

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

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

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

     transp     = "TRANSP" tranparam ":" transvalue CRLF

     tranparam  = *(";" xparam)

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

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

         TRANSP:TRANSPARENT

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

         TRANSP:OPAQUE

3.8.3.  Time Zone Component Properties

   The following properties specify time zone information in calendar
   components.





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3.8.3.1.  Time Zone Identifier

   Property Name: TZID

   Purpose: This property specifies the text value that uniquely
      identifies the "VTIMEZONE" calendar component.

   Value Type: TEXT

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

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



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

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

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

         tzidpropparam      = *(";" xparam)

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

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

         TZID:US-Eastern

         TZID:California-Los_Angeles




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

         TZID:/US-New_York-New_York

3.8.3.2.  Time Zone Name

   Property Name: TZNAME

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

   Value Type: TEXT

   Property Parameters: Non-standard and language property parameters
      can be specified on this property.

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

   Description: This property may be specified in multiple languages; in
      order to provide for different language requirements.

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

         tzname     = "TZNAME" tznparam ":" text CRLF

         tznparam   = *(

                    ; the following is optional,
                    ; but MUST NOT occur more than once

                    (";" languageparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

   Example: The following are example of this property:

         TZNAME:EST







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      The following is an example of this property when two different
      languages for the time zone name are specified:

         TZNAME;LANGUAGE=en:EST
         TZNAME;LANGUAGE=fr-CA:HNE

3.8.3.3.  Time Zone Offset From

   Property Name: TZOFFSETFROM

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

   Value Type: UTC-OFFSET

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

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

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

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

         frmparam   = *(";" xparam)

   Example: The following are examples of this property:

         TZOFFSETFROM:-0500

         TZOFFSETFROM:+1345







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3.8.3.4.  Time Zone Offset To

   Property Name: TZOFFSETTO

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

   Value Type: UTC-OFFSET

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

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

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

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

         toparam    = *(";" xparam)

   Example: The following are examples of this property:

         TZOFFSETTO:-0400

         TZOFFSETTO:+1245

3.8.3.5.  Time Zone URL

   Property Name: TZURL

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

   Value Type: URI







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   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

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

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

         tzurl      = "TZURL" tzurlparam ":" uri CRLF

         tzurlparam = *(";" xparam)

   Example: The following is an example of this property:

         TZURL:http://timezones.r.us.net/tz/US-California-Los_Angeles

3.8.4.  Relationship Component Properties

   The following properties specify relationship information in calendar
   components.

3.8.4.1.  Attendee

   Property Name: ATTENDEE

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

   Value Type: CAL-ADDRESS

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

   Conformance: This property MUST be specified in an iCalendar object
      that specifies a group scheduled calendar entity.  This property
      MUST NOT be specified in an iCalendar object when publishing the
      calendar information (e.g., NOT in an iCalendar object that
      specifies the publication of a calendar user's busy time, event,



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      to-do or journal).  This property is not specified in an iCalendar
      object that specifies only a time zone definition or that defines
      calendar entities that are not group scheduled entities, but are
      entities only on a single user's calendar.

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

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

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

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

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














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

         attparam   = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" cutypeparam) / (";"memberparam) /
                    (";" roleparam) / (";" partstatparam) /
                    (";" rsvpparam) / (";" deltoparam) /
                    (";" delfromparam) / (";" sentbyparam) /
                    (";"cnparam) / (";" dirparam) /
                    (";" languageparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

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

     ORGANIZER:MAILTO:jsmith@host1.com
     ATTENDEE;MEMBER="MAILTO:DEV-GROUP@host2.com":
      MAILTO:joecool@host2.com
     ATTENDEE;DELEGATED-FROM="MAILTO:immud@host3.com":
      MAILTO:ildoit@host1.com

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

     ORGANIZER:MAILTO:jsmith@host1.com
     ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=TENTATIVE;CN=Henry Cabot
      :MAILTO:hcabot@host2.com
     ATTENDEE;ROLE=REQ-PARTICIPANT;DELEGATED-FROM="MAILTO:bob@host.com"
      ;PARTSTAT=ACCEPTED;CN=Jane Doe:MAILTO:jdoe@host1.com

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

     ATTENDEE;CN=John Smith;DIR="ldap://host.com:6666/o=eDABC%
      20Industries,c=3DUS??(cn=3DBJim%20Dolittle)":MAILTO:jimdo@
      host1.com






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

     ORGANIZER;CN=John Smith:MAILTO:jsmith@host.com
     ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=TENTATIVE;DELEGATED-FROM=
      "MAILTO:iamboss@host2.com";CN=Henry Cabot:MAILTO:hcabot@
      host2.com
     ATTENDEE;ROLE=NON-PARTICIPANT;PARTSTAT=DELEGATED;DELEGATED-TO=
      "MAILTO:hcabot@host2.com";CN=The Big Cheese:MAILTO:iamboss
      @host2.com
     ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED;CN=Jane Doe
      :MAILTO:jdoe@host1.com

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

     ATTENDEE;SENT-BY=MAILTO:jan_doe@host1.com;CN=John Smith:MAILTO:
      jsmith@host1.com

3.8.4.2.  Contact

   Property Name: CONTACT

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

   Value Type: TEXT

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

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

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

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









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         contact    = "CONTACT" contparam ":" text CRLF

         contparam  = *(
                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" altrepparam) / (";" languageparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

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

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

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

     CONTACT;ALTREP="ldap://host.com:6666/o=3DABC%20Industries\,
      c=3DUS??(cn=3DBJim%20Dolittle)":Jim Dolittle\, ABC Industries\,
      +1-919-555-1234

      The following is an example of this property with an alternate
      representation of a MIME body part containing the contact
      information, such as a vCard [RFC2426] embedded in a [MIME-DIR]
      content-type:

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

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

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

3.8.4.3.  Organizer







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   Property Name: ORGANIZER

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

   Value Type: CAL-ADDRESS

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

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

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

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

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














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

         orgparam   = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" cnparam) / (";" dirparam) / (";" sentbyparam) /
                    (";" languageparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

   Example: The following is an example of this property:

       ORGANIZER;CN=John Smith:MAILTO:jsmith@host1.com

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

       ORGANIZER;CN=JohnSmith;DIR="ldap://host.com:6666/o=3DDC%20Associ
        ates,c=3DUS??(cn=3DJohn%20Smith)":MAILTO:jsmith@host1.com

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

       ORGANIZER;SENT-BY="MAILTO:jane_doe@host.com":
        MAILTO:jsmith@host1.com

3.8.4.4.  Recurrence ID

   Property Name: RECURRENCE-ID

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






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   Value Type: The default value type for this property is DATE-TIME.
      The time format can be any of the valid forms defined for a DATE-
      TIME value type.  See DATE-TIME value type definition for specific
      interpretations of the various forms.  The value type can be set
      to DATE.

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

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

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

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

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

      The "RECURRENCE-ID" property is used in conjunction with the "UID"
      and "SEQUENCE" property to identify a particular instance of a
      recurring event, to-do or journal.  For a given pair of "UID" and
      "SEQUENCE" property values, the "RECURRENCE-ID" value for a
      recurrence instance is fixed.  When the definition of the
      recurrence set for a calendar component changes, and hence the
      "SEQUENCE" property value changes, the "RECURRENCE-ID" for a given
      recurrence instance might also change.The "RANGE" parameter is
      used to specify the effective range of recurrence instances from
      the instance specified by the "RECURRENCE-ID" property value.  The
      default value for the range parameter is the single recurrence
      instance only.  The value can also be "THISANDPRIOR" to indicate a
      range defined by the given recurrence instance and all prior
      instances or the value can be "THISANDFUTURE" to indicate a range
      defined by the given recurrence instance and all subsequent
      instances.

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






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

         ridparam   = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" "VALUE" "=" ("DATE-TIME" / "DATE)) /
                    (";" tzidparam) / (";" rangeparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

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

   Example: The following are examples of this property:

         RECURRENCE-ID;VALUE=DATE:19960401

         RECURRENCE-ID;RANGE=THISANDFUTURE:19960120T120000Z

3.8.4.5.  Related To

   Property Name: RELATED-TO

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

   Value Type: TEXT

   Property Parameters: Non-standard and relationship type property
      parameters can be specified on this property.

   Conformance: The property can be specified one or more times in the
      "VEVENT", "VTODO" or "VJOURNAL" calendar components.

   Description: The property value consists of the persistent, globally
      unique identifier of another calendar component.  This value would
      be represented in a calendar component by the "UID" property.







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      By default, the property value points to another calendar
      component that has a PARENT relationship to the referencing
      object.  The "RELTYPE" property parameter is used to either
      explicitly state the default PARENT relationship type to the
      referenced calendar component or to override the default PARENT
      relationship type and specify either a CHILD or SIBLING
      relationship.  The PARENT relationship indicates that the calendar
      component is a subordinate of the referenced calendar component.
      The CHILD relationship indicates that the calendar component is a
      superior of the referenced calendar component.  The SIBLING
      relationship indicates that the calendar component is a peer of
      the referenced calendar component.

      Changes to a calendar component referenced by this property can
      have an implicit impact on the related calendar component.  For
      example, if a group event changes its start or end date or time,
      then the related, dependent events will need to have their start
      and end dates changed in a corresponding way.  Similarly, if a
      PARENT calendar component is canceled or deleted, then there is an
      implied impact to the related CHILD calendar components.  This
      property is intended only to provide information on the
      relationship of calendar components.  It is up to the target
      calendar system to maintain any property implications of this
      relationship.

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

         related    = "RELATED-TO" [relparam] ":" text CRLF

         relparam   = *(

                    ; the following is optional,
                    ; but MUST NOT occur more than once

                    (";" reltypeparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparm)

                    )

      The following is an example of this property:

         RELATED-TO:<jsmith.part7.19960817T083000.xyzMail@host3.com>

         RELATED-TO:<19960401-080045-4000F192713-0052@host1.com>



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3.8.4.6.  Uniform Resource Locator

   Property Name: URL

   Purpose: This property defines a Uniform Resource Locator (URL)
      associated with the iCalendar object.

   Value Type: URI

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

   Description: This property may be used in a calendar component to
      convey a location where a more dynamic rendition of the calendar
      information associated with the calendar component can be found.
      This memo does not attempt to standardize the form of the URI, nor
      the format of the resource pointed to by the property value.  If
      the URL property and Content-Location MIME header are both
      specified, they MUST point to the same resource.

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

         url        = "URL" urlparam ":" uri CRLF

         urlparam   = *(";" xparam)

   Example: The following is an example of this property:

         URL:http://abc.com/pub/calendars/jsmith/mytime.ics

3.8.4.7.  Unique Identifier

   Property Name: UID

   Purpose: This property defines the persistent, globally unique
      identifier for the calendar component.

   Value Type: TEXT

   Property Parameters: Non-standard property parameters can be
      specified on this property.







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   Conformance: The property MUST be specified in the "VEVENT", "VTODO",
      "VJOURNAL" or "VFREEBUSY" calendar components.

   Description: The UID itself MUST be a globally unique identifier.
      The generator of the identifier MUST guarantee that the identifier
      is unique.  There are several algorithms that can be used to
      accomplish this.  The identifier is RECOMMENDED to be the
      identical syntax to the [RFC0822] addr-spec.  A good method to
      assure uniqueness is to put the domain name or a domain literal IP
      address of the host on which the identifier was created on the
      right hand side of the "@", and on the left hand side, put a
      combination of the current calendar date and time of day (i.e.,
      formatted in as a DATE-TIME value) along with some other currently
      unique (perhaps sequential) identifier available on the system
      (for example, a process id number).  Using a date/time value on
      the left hand side and a domain name or domain literal on the
      right hand side makes it possible to guarantee uniqueness since no
      two hosts should be using the same domain name or IP address at
      the same time.  Though other algorithms will work, it is
      RECOMMENDED that the right hand side contain some domain
      identifier (either of the host itself or otherwise) such that the
      generator of the message identifier can guarantee the uniqueness
      of the left hand side within the scope of that domain.

      This is the method for correlating scheduling messages with the
      referenced "VEVENT", "VTODO", or "VJOURNAL" calendar component.

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

      This property is an important method for group scheduling
      applications to match requests with later replies, modifications
      or deletion requests.  Calendaring and scheduling applications
      MUST generate this property in "VEVENT", "VTODO" and "VJOURNAL"
      calendar components to assure interoperability with other group
      scheduling applications.  This identifier is created by the
      calendar system that generates an iCalendar object.

      Implementations MUST be able to receive and persist values of at
      least 255 characters for this property.

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

         uid        = "UID" uidparam ":" text CRLF




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         uidparam   = *(";" xparam)

   Example: The following is an example of this property:

         UID:19960401T080045Z-4000F192713-0052@host1.com

3.8.5.  Recurrence Component Properties

   The following properties specify recurrence information in calendar
   components.

3.8.5.1.  Exception Date/Times

   Property Name: EXDATE

   Purpose: This property defines the list of date/time exceptions for a
      recurring calendar component.

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

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

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

   Description: The exception dates, if specified, are used in computing
      the recurrence set.  The recurrence set is the complete set of
      recurrence instances for a calendar component.  The recurrence set
      is generated by considering the initial "DTSTART" property along
      with the "RRULE", "RDATE", "EXDATE" and "EXRULE" properties
      contained within the iCalendar object.  The "DTSTART" property
      defines the first instance in the recurrence set.  Multiple
      instances of the "RRULE" and "EXRULE" properties can also be
      specified to define more sophisticated recurrence sets.  The final
      recurrence set is generated by gathering all of the start date-
      times generated by any of the specified "RRULE" and "RDATE"
      properties, and then excluding any start date and times which fall
      within the union of start date and times generated by any
      specified "EXRULE" and "EXDATE" properties.  This implies that
      start date and times within exclusion related properties (i.e.,
      "EXDATE" and "EXRULE") take precedence over those specified by
      inclusion properties (i.e., "RDATE" and "RRULE").  Where duplicate
      instances are generated by the "RRULE" and "RDATE" properties,
      only one recurrence is considered.  Duplicate instances are
      ignored.




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      The "EXDATE" property can be used to exclude the value specified
      in "DTSTART".  However, in such cases the original "DTSTART" date
      MUST still be maintained by the calendaring and scheduling system
      because the original "DTSTART" value has inherent usage
      dependencies by other properties such as the "RECURRENCE-ID".

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

         exdate     = "EXDATE" exdtparam ":" exdtval *("," exdtval) CRLF

         exdtparam  = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                    (";" "VALUE" "=" ("DATE-TIME" / "DATE")) /

                    (";" tzidparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

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

   Example: The following is an example of this property:

         EXDATE:19960402T010000Z,19960403T010000Z,19960404T010000Z

3.8.5.2.  Exception Rule

   Property Name: EXRULE

   Purpose: This property defines a rule or repeating pattern for an
      exception to a recurrence set.

   Value Type: RECUR

   Property Parameters: Non-standard property parameters can be
      specified on this property.







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

   Description: The exception rule, if specified, is used in computing
      the recurrence set.  The recurrence set is the complete set of
      recurrence instances for a calendar component.  The recurrence set
      is generated by considering the initial "DTSTART" property along
      with the "RRULE", "RDATE", "EXDATE" and "EXRULE" properties
      contained within the iCalendar object.  The "DTSTART" defines the
      first instance in the recurrence set.  Multiple instances of the
      "RRULE" and "EXRULE" properties can also be specified to define
      more sophisticated recurrence sets.  The final recurrence set is
      generated by gathering all of the start date-times generated by
      any of the specified "RRULE" and "RDATE" properties, and excluding
      any start date and times which fall within the union of start date
      and times generated by any specified "EXRULE" and "EXDATE"
      properties.  This implies that start date and times within
      exclusion related properties (i.e., "EXDATE" and "EXRULE") take
      precedence over those specified by inclusion properties (i.e.,
      "RDATE" and "RRULE").  Where duplicate instances are generated by
      the "RRULE" and "RDATE" properties, only one recurrence is
      considered.  Duplicate instances are ignored.

      The "EXRULE" property can be used to exclude the value specified
      in "DTSTART".  However, in such cases the original "DTSTART" date
      MUST still be maintained by the calendaring and scheduling system
      because the original "DTSTART" value has inherent usage
      dependencies by other properties such as the "RECURRENCE-ID".

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

         exrule     = "EXRULE" exrparam ":" recur CRLF

         exrparam   = *(";" xparam)

   Example: The following are examples of this property.  Except every
      other week, on Tuesday and Thursday for 4 occurrences:

         EXRULE:FREQ=WEEKLY;COUNT=4;INTERVAL=2;BYDAY=TU,TH

      Except daily for 10 occurrences:

         EXRULE:FREQ=DAILY;COUNT=10








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      Except yearly in June and July for 8 occurrences:

         EXRULE:FREQ=YEARLY;COUNT=8;BYMONTH=6,7

3.8.5.3.  Recurrence Date/Times

   Property Name: RDATE

   Purpose: This property defines the list of date/times for a
      recurrence set.

   Value Type: The default value type for this property is DATE-TIME.
      The value type can be set to DATE or PERIOD.

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

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

   Description: This property can appear along with the "RRULE" property
      to define an aggregate set of repeating occurrences.  When they
      both appear in an iCalendar object, the recurring events are
      defined by the union of occurrences defined by both the "RDATE"
      and "RRULE".

      The recurrence dates, if specified, are used in computing the
      recurrence set.  The recurrence set is the complete set of
      recurrence instances for a calendar component.  The recurrence set
      is generated by considering the initial "DTSTART" property along
      with the "RRULE", "RDATE", "EXDATE" and "EXRULE" properties
      contained within the iCalendar object.  The "DTSTART" property
      defines the first instance in the recurrence set.  Multiple
      instances of the "RRULE" and "EXRULE" properties can also be
      specified to define more sophisticated recurrence sets.  The final
      recurrence set is generated by gathering all of the start date/
      times generated by any of the specified "RRULE" and "RDATE"
      properties, and excluding any start date/times which fall within
      the union of start date/times generated by any specified "EXRULE"
      and "EXDATE" properties.  This implies that start date/times
      within exclusion related properties (i.e., "EXDATE" and "EXRULE")
      take precedence over those specified by inclusion properties
      (i.e., "RDATE" and "RRULE").  Where duplicate instances are
      generated by the "RRULE" and "RDATE" properties, only one
      recurrence is considered.  Duplicate instances are ignored.






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

     rdate      = "RDATE" rdtparam ":" rdtval *("," rdtval) CRLF

     rdtparam   = *(

                ; the following are optional,
                ; but MUST NOT occur more than once

                (";" "VALUE" "=" ("DATE-TIME" / "DATE" / "PERIOD")) /
                (";" tzidparam) /

                ; the following is optional,
                ; and MAY occur more than once

                (";" xparam)

                )

     rdtval     = date-time / date / period
     ;Value MUST match value type

   Example: The following are examples of this property:

         RDATE:19970714T123000Z

         RDATE;TZID=US-EASTERN:19970714T083000

         RDATE;VALUE=PERIOD:19960403T020000Z/19960403T040000Z,
          19960404T010000Z/PT3H

         RDATE;VALUE=DATE:19970101,19970120,19970217,19970421
          19970526,19970704,19970901,19971014,19971128,19971129,19971225

3.8.5.4.  Recurrence Rule

   Property Name: RRULE

   Purpose: This property defines a rule or repeating pattern for
      recurring events, to-dos, or time zone definitions.

   Value Type: RECUR

   Property Parameters: Non-standard property parameters can be
      specified on this property.






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   Conformance: This property can be specified one or more times in
      recurring "VEVENT", "VTODO" and "VJOURNAL" calendar components.
      It can also be specified once in each STANDARD or DAYLIGHT sub-
      component of the "VTIMEZONE" calendar component.

   Description: The recurrence rule, if specified, is used in computing
      the recurrence set.  The recurrence set is the complete set of
      recurrence instances for a calendar component.  The recurrence set
      is generated by considering the initial "DTSTART" property along
      with the "RRULE", "RDATE", "EXDATE" and "EXRULE" properties
      contained within the iCalendar object.  The "DTSTART" property
      defines the first instance in the recurrence set.  Multiple
      instances of the "RRULE" and "EXRULE" properties can also be
      specified to define more sophisticated recurrence sets.  The final
      recurrence set is generated by gathering all of the start date/
      times generated by any of the specified "RRULE" and "RDATE"
      properties, and excluding any start date/times which fall within
      the union of start date/times generated by any specified "EXRULE"
      and "EXDATE" properties.  This implies that start date/times
      within exclusion related properties (i.e., "EXDATE" and "EXRULE")
      take precedence over those specified by inclusion properties
      (i.e., "RDATE" and "RRULE").  Where duplicate instances are
      generated by the "RRULE" and "RDATE" properties, only one
      recurrence is considered.  Duplicate instances are ignored.

      The "DTSTART" and "DTEND" property pair or "DTSTART" and
      "DURATION" property pair, specified within the iCalendar object
      defines the first instance of the recurrence.  When used with a
      recurrence rule, the "DTSTART" and "DTEND" properties MUST be
      specified in local time and the appropriate set of "VTIMEZONE"
      calendar components MUST be included.  For detail on the usage of
      the "VTIMEZONE" calendar component, see the "VTIMEZONE" calendar
      component definition.

      Any duration associated with the iCalendar object applies to all
      members of the generated recurrence set.  Any modified duration
      for specific recurrences MUST be explicitly specified using the
      "RDATE" property.

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

         rrule      = "RRULE" rrulparam ":" recur CRLF

         rrulparam  = *(";" xparam)







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   Example: All examples assume the Eastern United States time zone.

      Daily for 10 occurrences:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=DAILY;COUNT=10

         ==> (1997 9:00 AM EDT)September 2-11

      Daily until December 24, 1997:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=DAILY;UNTIL=19971224T000000Z

         ==> (1997 9:00 AM EDT)September 2-30;October 1-25
             (1997 9:00 AM EST)October 26-31;November 1-30;December 1-23

      Every other day - forever:

     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=DAILY;INTERVAL=2

     ==> (1997 9:00 AM EDT)September2,4,6,8...24,26,28,30;
          October 2,4,6...20,22,24
         (1997 9:00 AM EST)October 26,28,30;November 1,3,5,7...25,27,29;
          Dec 1,3,...

      Every 10 days, 5 occurrences:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=DAILY;INTERVAL=10;COUNT=5

         ==> (1997 9:00 AM EDT)September 2,12,22;October 2,12

      Everyday in January, for 3 years:

         DTSTART;TZID=US-Eastern:19980101T090000
         RRULE:FREQ=YEARLY;UNTIL=20000131T090000Z;
          BYMONTH=1;BYDAY=SU,MO,TU,WE,TH,FR,SA
         or
         RRULE:FREQ=DAILY;UNTIL=20000131T090000Z;BYMONTH=1

         ==> (1998 9:00 AM EDT)January 1-31
             (1999 9:00 AM EDT)January 1-31
             (2000 9:00 AM EDT)January 1-31






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      Weekly for 10 occurrences

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=WEEKLY;COUNT=10

         ==> (1997 9:00 AM EDT)September 2,9,16,23,30;October 7,14,21
             (1997 9:00 AM EST)October 28;November 4

      Weekly until December 24, 1997

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=WEEKLY;UNTIL=19971224T000000Z

         ==> (1997 9:00 AM EDT)September 2,9,16,23,30;October 7,14,21
             (1997 9:00 AM EST)October 28;November 4,11,18,25;
                               December 2,9,16,23

      Every other week - forever:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=WEEKLY;INTERVAL=2;WKST=SU

         ==> (1997 9:00 AM EDT)September 2,16,30;October 14
             (1997 9:00 AM EST)October 28;November 11,25;December 9,23
             (1998 9:00 AM EST)January 6,20;February
         ...

      Weekly on Tuesday and Thursday for 5 weeks:

      DTSTART;TZID=US-Eastern:19970902T090000
      RRULE:FREQ=WEEKLY;UNTIL=19971007T000000Z;WKST=SU;BYDAY=TU,TH
      or

      RRULE:FREQ=WEEKLY;COUNT=10;WKST=SU;BYDAY=TU,TH

      ==> (1997 9:00 AM EDT)September 2,4,9,11,16,18,23,25,30;October 2

      Every other week on Monday, Wednesday and Friday until December
      24, 1997, but starting on Tuesday, September 2, 1997:

     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;UNTIL=19971224T000000Z;WKST=SU;
      BYDAY=MO,WE,FR

     ==> (1997 9:00 AM EDT)September 2,3,5,15,17,19,29;October
     1,3,13,15,17
         (1997 9:00 AM EST)October 27,29,31;November 10,12,14,24,26,28;
                           December 8,10,12,22



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      Every other week on Tuesday and Thursday, for 8 occurrences:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=8;WKST=SU;BYDAY=TU,TH

         ==> (1997 9:00 AM EDT)September 2,4,16,18,30;October 2,14,16

      Monthly on the 1st Friday for ten occurrences:

         DTSTART;TZID=US-Eastern:19970905T090000
         RRULE:FREQ=MONTHLY;COUNT=10;BYDAY=1FR

         ==> (1997 9:00 AM EDT)September 5;October 3
             (1997 9:00 AM EST)November 7;Dec 5
             (1998 9:00 AM EST)January 2;February 6;March 6;April 3
             (1998 9:00 AM EDT)May 1;June 5

      Monthly on the 1st Friday until December 24, 1997:

         DTSTART;TZID=US-Eastern:19970905T090000
         RRULE:FREQ=MONTHLY;UNTIL=19971224T000000Z;BYDAY=1FR

         ==> (1997 9:00 AM EDT)September 5;October 3
             (1997 9:00 AM EST)November 7;December 5

      Every other month on the 1st and last Sunday of the month for 10
      occurrences:

         DTSTART;TZID=US-Eastern:19970907T090000
         RRULE:FREQ=MONTHLY;INTERVAL=2;COUNT=10;BYDAY=1SU,-1SU

         ==> (1997 9:00 AM EDT)September 7,28
             (1997 9:00 AM EST)November 2,30
             (1998 9:00 AM EST)January 4,25;March 1,29
             (1998 9:00 AM EDT)May 3,31

      Monthly on the second to last Monday of the month for 6 months:

         DTSTART;TZID=US-Eastern:19970922T090000
         RRULE:FREQ=MONTHLY;COUNT=6;BYDAY=-2MO

         ==> (1997 9:00 AM EDT)September 22;October 20
             (1997 9:00 AM EST)November 17;December 22
             (1998 9:00 AM EST)January 19;February 16







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      Monthly on the third to the last day of the month, forever:

         DTSTART;TZID=US-Eastern:19970928T090000
         RRULE:FREQ=MONTHLY;BYMONTHDAY=-3

         ==> (1997 9:00 AM EDT)September 28
             (1997 9:00 AM EST)October 29;November 28;December 29
             (1998 9:00 AM EST)January 29;February 26
         ...

      Monthly on the 2nd and 15th of the month for 10 occurrences:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=MONTHLY;COUNT=10;BYMONTHDAY=2,15

         ==> (1997 9:00 AM EDT)September 2,15;October 2,15
             (1997 9:00 AM EST)November 2,15;December 2,15
             (1998 9:00 AM EST)January 2,15

      Monthly on the first and last day of the month for 10 occurrences:

         DTSTART;TZID=US-Eastern:19970930T090000
         RRULE:FREQ=MONTHLY;COUNT=10;BYMONTHDAY=1,-1

         ==> (1997 9:00 AM EDT)September 30;October 1
             (1997 9:00 AM EST)October 31;November 1,30;December 1,31
             (1998 9:00 AM EST)January 1,31;February 1

      Every 18 months on the 10th thru 15th of the month for 10
      occurrences:

     DTSTART;TZID=US-Eastern:19970910T090000
     RRULE:FREQ=MONTHLY;INTERVAL=18;COUNT=10;BYMONTHDAY=10,11,12,13,14,
      15

     ==> (1997 9:00 AM EDT)September 10,11,12,13,14,15
         (1999 9:00 AM EST)March 10,11,12,13

      Every Tuesday, every other month:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=MONTHLY;INTERVAL=2;BYDAY=TU

         ==> (1997 9:00 AM EDT)September 2,9,16,23,30
             (1997 9:00 AM EST)November 4,11,18,25
             (1998 9:00 AM EST)January 6,13,20,27;March 3,10,17,24,31
         ...




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      Yearly in June and July for 10 occurrences:

       DTSTART;TZID=US-Eastern:19970610T090000
       RRULE:FREQ=YEARLY;COUNT=10;BYMONTH=6,7
       ==> (1997 9:00 AM EDT)June 10;July 10
           (1998 9:00 AM EDT)June 10;July 10
           (1999 9:00 AM EDT)June 10;July 10
           (2000 9:00 AM EDT)June 10;July 10
           (2001 9:00 AM EDT)June 10;July 10
       Note: Since none of the BYDAY, BYMONTHDAY or BYYEARDAY components
       are specified, the day is gotten from DTSTART

      Every other year on January, February, and March for 10
      occurrences:

         DTSTART;TZID=US-Eastern:19970310T090000
         RRULE:FREQ=YEARLY;INTERVAL=2;COUNT=10;BYMONTH=1,2,3

         ==> (1997 9:00 AM EST)March 10
             (1999 9:00 AM EST)January 10;February 10;March 10
             (2001 9:00 AM EST)January 10;February 10;March 10
             (2003 9:00 AM EST)January 10;February 10;March 10

      Every 3rd year on the 1st, 100th and 200th day for 10 occurrences:

         DTSTART;TZID=US-Eastern:19970101T090000
         RRULE:FREQ=YEARLY;INTERVAL=3;COUNT=10;BYYEARDAY=1,100,200

         ==> (1997 9:00 AM EST)January 1
             (1997 9:00 AM EDT)April 10;July 19
             (2000 9:00 AM EST)January 1
             (2000 9:00 AM EDT)April 9;July 18
             (2003 9:00 AM EST)January 1
             (2003 9:00 AM EDT)April 10;July 19
             (2006 9:00 AM EST)January 1

      Every 20th Monday of the year, forever:

         DTSTART;TZID=US-Eastern:19970519T090000
         RRULE:FREQ=YEARLY;BYDAY=20MO

         ==> (1997 9:00 AM EDT)May 19
             (1998 9:00 AM EDT)May 18
             (1999 9:00 AM EDT)May 17
         ...






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      Monday of week number 20 (where the default start of the week is
      Monday), forever:

         DTSTART;TZID=US-Eastern:19970512T090000
         RRULE:FREQ=YEARLY;BYWEEKNO=20;BYDAY=MO

         ==> (1997 9:00 AM EDT)May 12
             (1998 9:00 AM EDT)May 11
             (1999 9:00 AM EDT)May 17
         ...

      Every Thursday in March, forever:

         DTSTART;TZID=US-Eastern:19970313T090000
         RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=TH

         ==> (1997 9:00 AM EST)March 13,20,27
             (1998 9:00 AM EST)March 5,12,19,26
             (1999 9:00 AM EST)March 4,11,18,25
         ...

      Every Thursday, but only during June, July, and August, forever:

         DTSTART;TZID=US-Eastern:19970605T090000
         RRULE:FREQ=YEARLY;BYDAY=TH;BYMONTH=6,7,8

         ==> (1997 9:00 AM EDT)June 5,12,19,26;July 3,10,17,24,31;
                           August 7,14,21,28
             (1998 9:00 AM EDT)June 4,11,18,25;July 2,9,16,23,30;
                           August 6,13,20,27
             (1999 9:00 AM EDT)June 3,10,17,24;July 1,8,15,22,29;
                           August 5,12,19,26
         ...

      Every Friday the 13th, forever:

         DTSTART;TZID=US-Eastern:19970902T090000
         EXDATE;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=MONTHLY;BYDAY=FR;BYMONTHDAY=13

         ==> (1998 9:00 AM EST)February 13;March 13;November 13
             (1999 9:00 AM EDT)August 13
             (2000 9:00 AM EDT)October 13
         ...







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      The first Saturday that follows the first Sunday of the month,
      forever:

         DTSTART;TZID=US-Eastern:19970913T090000
         RRULE:FREQ=MONTHLY;BYDAY=SA;BYMONTHDAY=7,8,9,10,11,12,13

         ==> (1997 9:00 AM EDT)September 13;October 11
             (1997 9:00 AM EST)November 8;December 13
             (1998 9:00 AM EST)January 10;February 7;March 7
             (1998 9:00 AM EDT)April 11;May 9;June 13...
         ...

      Every four years, the first Tuesday after a Monday in November,
      forever (U.S. Presidential Election day):

     DTSTART;TZID=US-Eastern:19961105T090000
     RRULE:FREQ=YEARLY;INTERVAL=4;BYMONTH=11;BYDAY=TU;BYMONTHDAY=2,3,4,
      5,6,7,8

     ==> (1996 9:00 AM EST)November 5
         (2000 9:00 AM EST)November 7
         (2004 9:00 AM EST)November 2
     ...

      The 3rd instance into the month of one of Tuesday, Wednesday or
      Thursday, for the next 3 months:

         DTSTART;TZID=US-Eastern:19970904T090000
         RRULE:FREQ=MONTHLY;COUNT=3;BYDAY=TU,WE,TH;BYSETPOS=3

         ==> (1997 9:00 AM EDT)September 4;October 7
             (1997 9:00 AM EST)November 6

      The 2nd to last weekday of the month:

         DTSTART;TZID=US-Eastern:19970929T090000
         RRULE:FREQ=MONTHLY;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=-2

         ==> (1997 9:00 AM EDT)September 29
             (1997 9:00 AM EST)October 30;November 27;December 30
             (1998 9:00 AM EST)January 29;February 26;March 30
         ...

      Every 3 hours from 9:00 AM to 5:00 PM on a specific day:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=HOURLY;INTERVAL=3;UNTIL=19970902T170000Z




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         ==> (September 2, 1997 EDT)09:00,12:00,15:00

      Every 15 minutes for 6 occurrences:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=MINUTELY;INTERVAL=15;COUNT=6

         ==> (September 2, 1997 EDT)09:00,09:15,09:30,09:45,10:00,10:15

      Every hour and a half for 4 occurrences:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=MINUTELY;INTERVAL=90;COUNT=4

         ==> (September 2, 1997 EDT)09:00,10:30;12:00;13:30

      Every 20 minutes from 9:00 AM to 4:40 PM every day:

         DTSTART;TZID=US-Eastern:19970902T090000
         RRULE:FREQ=DAILY;BYHOUR=9,10,11,12,13,14,15,16;BYMINUTE=0,20,40
         or
         RRULE:FREQ=MINUTELY;INTERVAL=20;BYHOUR=9,10,11,12,13,14,15,16

         ==> (September 2, 1997 EDT)9:00,9:20,9:40,10:00,10:20,
                                    ... 16:00,16:20,16:40
             (September 3, 1997 EDT)9:00,9:20,9:40,10:00,10:20,
                                   ...16:00,16:20,16:40
         ...

      An example where the days generated makes a difference because of
      WKST:

         DTSTART;TZID=US-Eastern:19970805T090000
         RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=4;BYDAY=TU,SU;WKST=MO

         ==> (1997 EDT)Aug 5,10,19,24

         changing only WKST from MO to SU, yields different results...

         DTSTART;TZID=US-Eastern:19970805T090000
         RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=4;BYDAY=TU,SU;WKST=SU
         ==> (1997 EDT)August 5,17,19,31

3.8.6.  Alarm Component Properties

   The following properties specify alarm information in calendar
   components.




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3.8.6.1.  Action

   Property Name: ACTION

   Purpose: This property defines the action to be invoked when an alarm
      is triggered.

   Value Type: TEXT

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

   Description: Each "VALARM" calendar component has a particular type
      of action associated with it.  This property specifies the type of
      action

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

       action     = "ACTION" actionparam ":" actionvalue CRLF

       actionparam        = *(";" xparam)

       actionvalue        = "AUDIO" / "DISPLAY" / "EMAIL" / "PROCEDURE"
                          / iana-token / x-name

   Example: The following are examples of this property in a "VALARM"
      calendar component:

         ACTION:AUDIO

         ACTION:DISPLAY

         ACTION:PROCEDURE

3.8.6.2.  Repeat Count

   Property Name: REPEAT

   Purpose: This property defines the number of time the alarm should be
      repeated, after the initial trigger.

   Value Type: INTEGER






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   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

   Description: If the alarm triggers more than once, then this property
      MUST be specified along with the "DURATION" property.

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

         repeatcnt  = "REPEAT" repparam ":" integer CRLF
         ;Default is "0", zero.

         repparam   = *(";" xparam)

   Example: The following is an example of this property for an alarm
      that repeats 4 additional times with a 5 minute delay after the
      initial triggering of the alarm:

         REPEAT:4
         DURATION:PT5M

3.8.6.3.  Trigger

   Property Name: TRIGGER

   Purpose: This property specifies when an alarm will trigger.

   Value Type: The default value type is DURATION.  The value type can
      be set to a DATE-TIME value type, in which case the value MUST
      specify a UTC formatted DATE-TIME value.

   Property Parameters: Non-standard, value data type, time zone
      identifier or trigger relationship property parameters can be
      specified on this property.  The trigger relationship property
      parameter MUST only be specified when the value type is DURATION.

   Conformance: This property MUST be specified in the "VALARM" calendar
      component.

   Description: Within the "VALARM" calendar component, this property
      defines when the alarm will trigger.  The default value type is
      DURATION, specifying a relative time for the trigger of the alarm.
      The default duration is relative to the start of an event or to-do
      that the alarm is associated with.  The duration can be explicitly
      set to trigger from either the end or the start of the associated
      event or to-do with the "RELATED" parameter.  A value of START



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      will set the alarm to trigger off the start of the associated
      event or to-do.  A value of END will set the alarm to trigger off
      the end of the associated event or to-do.

      Either a positive or negative duration may be specified for the
      "TRIGGER" property.  An alarm with a positive duration is
      triggered after the associated start or end of the event or to-do.
      An alarm with a negative duration is triggered before the
      associated start or end of the event or to-do.

      The "RELATED" property parameter is not valid if the value type of
      the property is set to DATE-TIME (i.e., for an absolute date and
      time alarm trigger).  If a value type of DATE-TIME is specified,
      then the property value MUST be specified in the UTC time format.
      If an absolute trigger is specified on an alarm for a recurring
      event or to-do, then the alarm will only trigger for the specified
      absolute date/time, along with any specified repeating instances.

      If the trigger is set relative to START, then the "DTSTART"
      property MUST be present in the associated "VEVENT" or "VTODO"
      calendar component.  If an alarm is specified for an event with
      the trigger set relative to the END, then the "DTEND" property or
      the "DSTART" and "DURATION' properties MUST be present in the
      associated "VEVENT" calendar component.  If the alarm is specified
      for a to-do with a trigger set relative to the END, then either
      the "DUE" property or the "DTSTART" and "DURATION" properties MUST
      be present in the associated "VTODO" calendar component.

      Alarms specified in an event or to-do which is defined in terms of
      a DATE value type will be triggered relative to 00:00:00 UTC on
      the specified date.  For example, if "DTSTART:19980205, then the
      duration trigger will be relative to19980205T000000Z.

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

















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         trigger    = "TRIGGER" (trigrel / trigabs)

         trigrel    = *(

                    ; the following are optional,
                    ; but MUST NOT occur more than once

                      (";" "VALUE" "=" "DURATION") /
                      (";" trigrelparam) /

                    ; the following is optional,
                    ; and MAY occur more than once

                      (";" xparam)
                      ) ":"  dur-value

         trigabs    = 1*(

                    ; the following is REQUIRED,
                    ; but MUST NOT occur more than once

                      (";" "VALUE" "=" "DATE-TIME") /

                    ; the following is optional,
                    ; and MAY occur more than once

                      (";" xparam)

                      ) ":" date-time

   Example: A trigger set 15 minutes prior to the start of the event or
      to-do.

         TRIGGER:-P15M

      A trigger set 5 minutes after the end of the event or to-do.

         TRIGGER;RELATED=END:P5M

      A trigger set to an absolute date/time.

         TRIGGER;VALUE=DATE-TIME:19980101T050000Z

3.8.7.  Change Management Component Properties

   The following properties specify change management information in
   calendar components.




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3.8.7.1.  Date/Time Created

   Property Name: CREATED

   Purpose: This property specifies the date and time that the calendar
      information was created by the calendar user agent in the calendar
      store.

         Note: This is analogous to the creation date and time for a
         file in the file system.

   Value Type: DATE-TIME

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

   Description: The date and time is a UTC value.

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

         created    = "CREATED" creaparam ":" date-time CRLF

         creaparam  = *(";" xparam)

   Example: The following is an example of this property:

         CREATED:19960329T133000Z

3.8.7.2.  Date/Time Stamp

   Property Name: DTSTAMP

   Purpose: The property indicates the date/time that the instance of
      the iCalendar object was created.

   Value Type: DATE-TIME

   Property Parameters: Non-standard property parameters can be
      specified on this property.

   Conformance: This property MUST be included in the "VEVENT", "VTODO",
      "VJOURNAL" or "VFREEBUSY" calendar components.






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   Description: The value MUST be specified in the UTC time format.

      This property is also useful to protocols such as [I-D.ietf-
      calsify-rfc2447bis] that have inherent latency issues with the
      delivery of content.  This property will assist in the proper
      sequencing of messages containing iCalendar objects.

      This property is different than the "CREATED" and "LAST-MODIFIED"
      properties.  These two properties are used to specify when the
      particular calendar data in the calendar store was created and
      last modified.  This is different than when the iCalendar object
      representation of the calendar service information was created or
      last modified.

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

         dtstamp    = "DTSTAMP" stmparam ":" date-time CRLF

         stmparam   = *(";" xparam)

   Example:

         DTSTAMP:19971210T080000Z

3.8.7.3.  Last Modified

   Property Name: LAST-MODIFIED

   Purpose: The property specifies the date and time that the
      information associated with the calendar component was last
      revised in the calendar store.

         Note: This is analogous to the modification date and time for a
         file in the file system.

   Value Type: DATE-TIME

   Property Parameters: Non-standard property parameters can be
      specified on this property.

   Conformance: This property can be specified in the "EVENT", "VTODO",
      "VJOURNAL" or "VTIMEZONE" calendar components.

   Description: The property value MUST be specified in the UTC time
      format.






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

         last-mod   = "LAST-MODIFIED" lstparam ":" date-time CRLF

         lstparam   = *(";" xparam)

   Example: The following is are examples of this property:

                   LAST-MODIFIED:19960817T133000Z

3.8.7.4.  Sequence Number

   Property Name: SEQUENCE

   Purpose: This property defines the revision sequence number of the
      calendar component within a sequence of revisions.

   Value Type: integer

   Property Parameters: Non-standard property parameters can be
      specified on this property.

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

   Description: When a calendar component is created, its sequence
      number is zero (US-ASCII decimal 48).  It is monotonically
      incremented by the "Organizer's" CUA each time the "Organizer"
      makes a significant revision to the calendar component.  When the
      "Organizer" makes changes to one of the following properties, the
      sequence number MUST be incremented:

         "DTSTART"

         "DTEND"

         "DUE"

         "RDATE"

         "RRULE"

         "EXDATE"

         "EXRULE"






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         "STATUS"

      In addition, changes made by the "Organizer" to other properties
      can also force the sequence number to be incremented.  The
      "Organizer" CUA MUST increment the sequence number when ever it
      makes changes to properties in the calendar component that the
      "Organizer" deems will jeopardize the validity of the
      participation status of the "Attendees".  For example, changing
      the location of a meeting from one locale to another distant
      locale could effectively impact the participation status of the
      "Attendees".

      The "Organizer" includes this property in an iCalendar object that
      it sends to an "Attendee" to specify the current version of the
      calendar component.

      The "Attendee" includes this property in an iCalendar object that
      it sends to the "Organizer" to specify the version of the calendar
      component that the "Attendee" is referring to.

      A change to the sequence number is not the mechanism that an
      "Organizer" uses to request a response from the "Attendees".  The
      "RSVP" parameter on the "ATTENDEE" property is used by the
      "Organizer" to indicate that a response from the "Attendees" is
      requested.

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

         seq = "SEQUENCE" seqparam ":" integer CRLF
         ; Default is "0"

         seqparam   = *(";" xparam)



   Example: The following is an example of this property for a calendar
      component that was just created by the "Organizer".

         SEQUENCE:0

      The following is an example of this property for a calendar
      component that has been revised two different times by the
      "Organizer".

         SEQUENCE:2






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3.8.8.  Miscellaneous Component Properties

   The following properties specify information about a number of
   miscellaneous features of calendar components.

3.8.8.1.  Non-standard Properties

   Property Name: Any property name with a "X-" prefix

   Purpose: This class of property provides a framework for defining
      non-standard properties.

   Value Type: TEXT

   Property Parameters: Non-standard and language property parameters
      can be specified on this property.

   Conformance: This property can be specified in any calendar
      component.

   Description: The MIME Calendaring and Scheduling Content Type
      provides a "standard mechanism for doing non-standard things".
      This extension support is provided for implementers to "push the
      envelope" on the existing version of the memo.  Extension
      properties are specified by property and/or property parameter
      names that have the prefix text of "X-" (the two character
      sequence: LATIN CAPITAL LETTER X character followed by the HYPEN-
      MINUS character).  It is recommended that vendors concatenate onto
      this sentinel another short prefix text to identify the vendor.
      This will facilitate readability of the extensions and minimize
      possible collision of names between different vendors.  User
      agents that support this content type are expected to be able to
      parse the extension properties and property parameters but can
      ignore them.

      At present, there is no registration authority for names of
      extension properties and property parameters.  The data type for
      this property is TEXT.  Optionally, the data type can be any of
      the other valid data types.

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

     x-prop     = x-name *(";" xparam) [";" languageparam] ":" text CRLF
        ; Lines longer than 75 octets should be folded







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   Example: The following might be the ABC vendor's extension for an
      audio-clip form of subject property:

     X-ABC-MMSUBJ;X-ABC-MMSUBJTYPE=wave:http://load.noise.org/mysubj.wav

3.8.8.2.  Request Status

   Property Name: REQUEST-STATUS

   Purpose: This property defines the status code returned for a
      scheduling request.

   Value Type: TEXT

   Property Parameters: Non-standard and language property parameters
      can be specified on this property.

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

   Description: This property is used to return status code information
      related to the processing of an associated iCalendar object.  The
      data type for this property is TEXT.

      The value consists of a short return status component, a longer
      return status description component, and optionally a status-
      specific data component.  The components of the value are
      separated by the SEMICOLON character (US-ASCII decimal 59).

      The short return status is a PERIOD character (US-ASCII decimal
      46) separated 3-tuple of integers.  For example, "3.1.1".  The
      successive levels of integers provide for a successive level of
      status code granularity.

      The following are initial classes for the return status code.
      Individual iCalendar object methods will define specific return
      status codes for these classes.  In addition, other classes for
      the return status code may be defined using the registration
      process defined later in this memo.












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        |==============+===============================================|
        | Short Return | Longer Return Status Description              |
        | Status Code  |                                               |
        |==============+===============================================|
        |    1.xx      | Preliminary success. This class of status     |
        |              | of status code indicates that the request has |
        |              | request has been initially processed but that |
        |              | completion is pending.                        |
        |==============+===============================================|
        |    2.xx      | Successful. This class of status code         |
        |              | indicates that the request was completed      |
        |              | successfuly. However, the exact status code   |
        |              | can indicate that a fallback has been taken.  |
        |==============+===============================================|
        |    3.xx      | Client Error. This class of status code       |
        |              | indicates that the request was not successful.|
        |              | The error is the result of either a syntax or |
        |              | a semantic error in the client formatted      |
        |              | request. Request should not be retried until  |
        |              | the condition in the request is corrected.    |
        |==============+===============================================|
        |    4.xx      | Scheduling Error. This class of status code   |
        |              | indicates that the request was not successful.|
        |              | Some sort of error occurred within the        |
        |              | calendaring and scheduling service, not       |
        |              | directly related to the request itself.       |
        |==============+===============================================|

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






















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         rstatus    = "REQUEST-STATUS" rstatparam ":"
                      statcode ";" statdesc [";" extdata]

         rstatparam = *(

                    ; the following is optional,
                    ; but MUST NOT occur more than once

                    (";" languageparm) /

                    ; the following is optional,
                    ; and MAY occur more than once

                    (";" xparam)

                    )

         statcode   = 1*DIGIT *("." 1*DIGIT)
         ;Hierarchical, numeric return status code

         statdesc   = text
         ;Textual status description

         extdata    = text
         ;Textual exception data. For example, the offending property
         ;name and value or complete property line.

   Example: The following are some possible examples of this property.

      The COMMA and SEMICOLON separator characters in the property value
      are BACKSLASH character escaped because they appear in a text
      value.

     REQUEST-STATUS:2.0;Success

     REQUEST-STATUS:3.1;Invalid property value;DTSTART:96-Apr-01

     REQUEST-STATUS:2.8; Success\, repeating event ignored. Scheduled
      as a single event.;RRULE:FREQ=WEEKLY\;INTERVAL=2

     REQUEST-STATUS:4.1;Event conflict. Date/time is busy.

     REQUEST-STATUS:3.7;Invalid calendar user;ATTENDEE:
      MAILTO:jsmith@host.com







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4.  iCalendar Object Examples

   The following examples are provided as an informational source of
   illustrative iCalendar objects consistent with this content type.

   The following example specifies a three-day conference that begins at
   8:00 AM EDT, September 18, 1996 and end at 6:00 PM EDT, September 20,
   1996.


        BEGIN:VCALENDAR
        PRODID:-//xyz Corp//NONSGML PDA Calendar Version 1.0//EN
        VERSION:2.0
        BEGIN:VEVENT
        DTSTAMP:19960704T120000Z
        UID:uid1@host.com
        ORGANIZER:MAILTO:jsmith@host.com
        DTSTART:19960918T143000Z
        DTEND:19960920T220000Z
        STATUS:CONFIRMED
        CATEGORIES:CONFERENCE
        SUMMARY:Networld+Interop Conference
        DESCRIPTION:Networld+Interop Conference
          and Exhibit\nAtlanta World Congress Center\n
         Atlanta, Georgia
        END:VEVENT
        END:VCALENDAR

   The following example specifies a group scheduled meeting that begin
   at 8:30 AM EST on March 12, 1998 and end at 9:30 AM EST on March 12,
   1998.  The "Organizer" has scheduled the meeting with one or more
   calendar users in a group.  A time zone specification for Eastern
   United States has been specified.


















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        BEGIN:VCALENDAR
        PRODID:-//RDU Software//NONSGML HandCal//EN
        VERSION:2.0
        BEGIN:VTIMEZONE
        TZID:US-Eastern
        BEGIN:STANDARD
        DTSTART:19981025T020000
        RDATE:19981025T020000
        TZOFFSETFROM:-0400
        TZOFFSETTO:-0500
        TZNAME:EST
        END:STANDARD
        BEGIN:DAYLIGHT
        DTSTART:19990404T020000
        RDATE:19990404T020000
        TZOFFSETFROM:-0500
        TZOFFSETTO:-0400
        TZNAME:EDT
        END:DAYLIGHT
        END:VTIMEZONE
        BEGIN:VEVENT
        DTSTAMP:19980309T231000Z
        UID:guid-1.host1.com
        ORGANIZER;ROLE=CHAIR:MAILTO:mrbig@host.com
        ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT;CUTYPE=GROUP:
         MAILTO:employee-A@host.com
        DESCRIPTION:Project XYZ Review Meeting
        CATEGORIES:MEETING
        CLASS:PUBLIC
        CREATED:19980309T130000Z
        SUMMARY:XYZ Project Review
        DTSTART;TZID=US-Eastern:19980312T083000
        DTEND;TZID=US-Eastern:19980312T093000
        LOCATION:1CP Conference Room 4350
        END:VEVENT
        END:VCALENDAR

   The following is an example of an iCalendar object passed in a MIME
   message with a single body part consisting of a "text/calendar"
   Content Type.











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        TO:jsmith@host1.com
        FROM:jdoe@host1.com
        MIME-VERSION:1.0
        MESSAGE-ID:<id3@host1.com>
        CONTENT-TYPE:text/calendar

        BEGIN:VCALENDAR
        METHOD:xyz
        VERSION:2.0
        PRODID:-//ABC Corporation//NONSGML My Product//EN
        BEGIN:VEVENT
        DTSTAMP:19970324T120000Z
        SEQUENCE:0
        UID:uid3@host1.com
        ORGANIZER:MAILTO:jdoe@host1.com
        ATTENDEE;RSVP=TRUE:MAILTO:jsmith@host1.com
        DTSTART:19970324T123000Z
        DTEND:19970324T210000Z
        CATEGORIES:MEETING,PROJECT
        CLASS:PUBLIC
        SUMMARY:Calendaring Interoperability Planning Meeting
        DESCRIPTION:Discuss how we can test c&s interoperability\n
         using iCalendar and other IETF standards.
        LOCATION:LDB Lobby
        ATTACH;FMTTYPE=application/postscript:ftp://xyzCorp.com/pub/
         conf/bkgrnd.ps
        END:VEVENT
        END:VCALENDAR

   The following is an example of a to-do due on April 15, 1998.  An
   audio alarm has been specified to remind the calendar user at noon,
   the day before the to-do is expected to be completed and repeat
   hourly, four additional times.  The to-do definition has been
   modified twice since it was initially created.

















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        BEGIN:VCALENDAR
        VERSION:2.0
        PRODID:-//ABC Corporation//NONSGML My Product//EN
        BEGIN:VTODO
        DTSTAMP:19980130T134500Z
        SEQUENCE:2
        UID:uid4@host1.com
        ORGANIZER:MAILTO:unclesam@us.gov
        ATTENDEE;PARTSTAT=ACCEPTED:MAILTO:jqpublic@host.com
        DUE:19980415T235959
        STATUS:NEEDS-ACTION
        SUMMARY:Submit Income Taxes
        BEGIN:VALARM
        ACTION:AUDIO
        TRIGGER:19980403T120000
        ATTACH;FMTTYPE=audio/basic:http://host.com/pub/audio-
         files/ssbanner.aud
        REPEAT:4
        DURATION:PT1H
        END:VALARM
        END:VTODO
        END:VCALENDAR

   The following is an example of a journal entry.

        BEGIN:VCALENDAR
        VERSION:2.0
        PRODID:-//ABC Corporation//NONSGML My Product//EN
        BEGIN:VJOURNAL
        DTSTAMP:19970324T120000Z
        UID:uid5@host1.com
        ORGANIZER:MAILTO:jsmith@host.com
        STATUS:DRAFT
        CLASS:PUBLIC
        CATEGORY:Project Report, XYZ, Weekly Meeting
        DESCRIPTION:Project xyz Review Meeting Minutes\n
         Agenda\n1. Review of project version 1.0 requirements.\n2.
        Definition
         of project processes.\n3. Review of project schedule.\n
         Participants: John Smith, Jane Doe, Jim Dandy\n-It was
          decided that the requirements need to be signed off by
          product marketing.\n-Project processes were accepted.\n
         -Project schedule needs to account for scheduled holidays
          and employee vacation time. Check with HR for specific
          dates.\n-New schedule will be distributed by Friday.\n-
         Next weeks meeting is cancelled. No meeting until 3/23.
        END:VJOURNAL
        END:VCALENDAR



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   The following is an example of published busy time information.  The
   iCalendar object might be placed in the network resource
   www.host.com/calendar/busytime/jsmith.ifb.

        BEGIN:VCALENDAR
        VERSION:2.0
        PRODID:-//RDU Software//NONSGML HandCal//EN
        BEGIN:VFREEBUSY
        ORGANIZER:MAILTO:jsmith@host.com
        DTSTART:19980313T141711Z
        DTEND:19980410T141711Z
        FREEBUSY:19980314T233000Z/19980315T003000Z
        FREEBUSY:19980316T153000Z/19980316T163000Z
        FREEBUSY:19980318T030000Z/19980318T040000Z
        URL:http://www.host.com/calendar/busytime/jsmith.ifb
        END:VFREEBUSY
        END:VCALENDAR


5.  Recommended Practices

   These recommended practices should be followed in order to assure
   consistent handling of the following cases for an iCalendar object.

   1.   Content lines longer than 75 octets SHOULD be folded.

   2.   A calendar entry with a "DTSTART" property but no "DTEND"
        property does not take up any time.  It is intended to represent
        an event that is associated with a given calendar date and time
        of day, such as an anniversary.  Since the event does not take
        up any time, it MUST NOT be used to record busy time no matter
        what the value for the "TRANSP" property.

   3.   When the "DTSTART" and "DTEND", for "VEVENT", "VJOURNAL" and
        "VFREEBUSY" calendar components, and "DTSTART" and "DUE", for
        "VTODO" calendar components, have the same value data type
        (e.g., DATE-TIME), they SHOULD specify values in the same time
        format (e.g., UTC time format).

   4.   When the combination of the "RRULE" and "RDATE" properties on an
        iCalendar object produces multiple instances having the same
        start date/time, they should be collapsed to, and considered as,
        a single instance.

   5.   When a calendar user receives multiple requests for the same
        calendar component (e.g., REQUEST for a "VEVENT" calendar
        component) as a result of being on multiple mailing lists
        specified by "ATTENDEE" properties in the request, they SHOULD



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        respond to only one of the requests.  The calendar user SHOULD
        also specify (using the "MEMBER" parameter of the "ATTENDEE"
        property) which mailing list they are a member of.

   6.   An implementation can truncate a "SUMMARY" property value to 255
        characters.

   7.   If seconds of the minute are not supported by an implementation,
        then a value of "00" SHOULD be specified for the seconds
        component in a time value.

   8.   If the value type parameter (VALUE=) contains an unknown value
        type, it SHOULD be treated as TEXT.

   9.   TZURL values SHOULD NOT be specified as a FILE URI type.  This
        URI form can be useful within an organization, but is
        problematic in the Internet.

   10.  Some possible English values for CATEGORIES property include
        "ANNIVERSARY", "APPOINTMENT", "BUSINESS", "EDUCATION",
        "HOLIDAY", "MEETING", "MISCELLANEOUS", "NON-WORKING HOURS", "NOT
        IN OFFICE", "PERSONAL", "PHONE CALL", "SICK DAY", "SPECIAL
        OCCASION", "TRAVEL", "VACATION".  Categories can be specified in
        any registered language.

   11.  Some possible English values for RESOURCES property include
        "CATERING", "CHAIRS", "COMPUTER PROJECTOR", "EASEL", "OVERHEAD
        PROJECTOR", "SPEAKER PHONE", "TABLE", "TV", "VCR", "VIDEO
        PHONE", "VEHICLE".  Resources can be specified in any registered
        language.


6.  Registration of Content Type Elements

   This section provides the process for registration of MIME
   Calendaring and Scheduling Content Type iCalendar object methods and
   new or modified properties.

6.1.  Registration of New and Modified iCalendar Object Methods

   New MIME Calendaring and Scheduling Content Type iCalendar object
   methods are registered by the publication of an IETF Request for
   Comments (RFC).  Changes to an iCalendar object method are registered
   by the publication of a revision of the RFC defining the method.

6.2.  Registration of New Properties

   This section defines procedures by which new properties or enumerated



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   property values for the MIME Calendaring and Scheduling Content Type
   can be registered with the IANA.  Non-IANA properties can be used by
   bilateral agreement, provided the associated properties names follow
   the "X-" convention.

   The procedures defined here are designed to allow public comment and
   review of new properties, while posing only a small impediment to the
   definition of new properties.

   Registration of a new property is accomplished by the following
   steps.

6.2.1.  Define the property

   A property is defined by completing the following template.

           To: ietf-calendar@imc.org

           Subject: Registration of text/calendar MIME property XXX

           Property name:

           Property purpose:

           Property value type(s):

           Property parameter (s):

           Conformance:

           Description:

           Format definition:

           Examples:

   The meaning of each field in the template is as follows.

   Property name: The name of the property, as it will appear in the
      body of an text/calendar MIME Content-Type "property: value" line
      to the left of the colon ":".

   Property purpose: The purpose of the property (e.g., to indicate a
      delegate for the event or to-do, etc.).  Give a short but clear
      description.






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   Property value type (s): Any of the valid value types for the
      property value needs to be specified.  The default value type also
      needs to be specified.  If a new value type is specified, it needs
      to be declared in this section.

   Property parameter (s): Any of the valid property parameters for the
      property needs to be specified.

   Conformance: The calendar components that the property can appear in
      needs to be specified.

   Description: Any special notes about the property, how it is to be
      used, etc.

   Format definition: The ABNF for the property definition needs to be
      specified.

   Examples: One or more examples of instances of the property needs to
      be specified.

6.2.2.  Post the Property definition

   The property description MUST be posted to the new property
   discussion list, ietf-calendar@imc.org.

6.2.3.  Allow a comment period

   Discussion on the new property MUST be allowed to take place on the
   list for a minimum of two weeks.  Consensus MUST be reached on the
   property before proceeding to the next step.

6.2.4.  Submit the property for approval

   Once the two-week comment period has elapsed, and the proposer is
   convinced consensus has been reached on the property, the
   registration application should be submitted to the Method Reviewer
   for approval.  The Method Reviewer is appointed to the Application
   Area Directors and can either accept or reject the property
   registration.  An accepted registration should be passed on by the
   Method Reviewer to the IANA for inclusion in the official IANA method
   registry.  The registration can be rejected for any of the following
   reasons. 1) Insufficient comment period; 2) Consensus not reached; 3)
   Technical deficiencies raised on the list or elsewhere have not been
   addressed.  The Method Reviewer's decision to reject a property can
   be appealed by the proposer to the IESG, or the objections raised can
   be addressed by the proposer and the property resubmitted.





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6.3.  Property Change Control

   Existing properties can be changed using the same process by which
   they were registered.

   1.  Define the change

   2.  Post the change

   3.  Allow a comment period

   4.  Submit the property for approval

   Note that the original author or any other interested party can
   propose a change to an existing property, but that such changes
   should only be proposed when there are serious omissions or errors in
   the published memo.  The Method Reviewer can object to a change if it
   is not backward compatible, but is not required to do so.

   Property definitions can never be deleted from the IANA registry, but
   properties which are no longer believed to be useful can be declared
   OBSOLETE by a change to their "intended use" field.


7.  Internationalization Considerations


8.  Security Considerations

   SPOOFING: In this memo, the "Organizer" is the only person authorized
      to make changes to an existing "VEVENT", "VTODO", "VJOURNAL"
      calendar component and redistribute the updates to the
      "Attendees".  An iCalendar object that maliciously changes or
      cancels an existing "VEVENT", "VTODO" or "VJOURNAL" or "VFREEBUSY"
      calendar component might be constructed by someone other than the
      "Organizer" and sent to the "Attendees".  In addition in this
      memo, other than the "Organizer", an "Attendee" of a "VEVENT",
      "VTODO", "VJOURNAL" calendar component is the only other person
      authorized to update any parameter associated with their
      "ATTENDEE" property and send it to the "Organizer".  An iCalendar
      object that maliciously changes the "ATTENDEE" parameters can be
      constructed by someone other than the real "Attendee" and sent to
      the "Organizer".

   PROCEDURAL ALARMS: An iCalendar object can be created that contains a
      "VEVENT" and "VTODO" calendar component with "VALARM" calendar
      components.  The "VALARM" calendar component can be of type
      PROCEDURE and can have an attachment containing some sort of



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      executable program.  Implementations that incorporate these types
      of alarms are subject to any virus or malicious attack that might
      occur as a result of executing the attachment.

   ATTACHMENTS: An iCalendar object can include references to Uniform
      Resource Locators that can be programmed resources.

      Implementers and users of this memo should be aware of the network
      security implications of accepting and parsing such information.
      In addition, the security considerations observed by
      implementations of electronic mail systems should be followed for
      this memo.


9.  IANA Consideration

9.1.  Media Type Registration Information

   The Calendaring and Scheduling Core Object Specification is intended
   for use as a MIME content type.  However, the implementation of the
   memo is in no way limited solely as a MIME content type.

   To: ietf-types@iana.org
   Subject: Registration of media type text/calendar

   Type name: text

   Subtype name: calendar

   Required parameters: none

   Optional parameters: charset, method, component and optinfo

      The "charset" parameter is defined in [RFC2046] for other body
      parts.  It is used to identify the default character set used
      within the body part.

      The "method" parameter is used to convey the iCalendar object
      method or transaction semantics for the calendaring and scheduling
      information.  It also is an identifier for the restricted set of
      properties and values that the iCalendar object consists of.  The
      parameter is to be used as a guide for applications interpreting
      the information contained within the body part.  It SHOULD NOT be
      used to exclude or require particular pieces of information unless
      the identified method definition specifically calls for this
      behavior.  Unless specifically forbidden by a particular method
      definition, a text/calendar content type can contain any set of
      properties permitted by the Calendaring and Scheduling Core Object



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      Specification.  The "method" parameter MUST be the same value as
      that specified in the "METHOD" component property in the iCalendar
      object.  If one is present, the other MUST also be present.

      The value for the "method" parameter is defined as follows:

     method  = 1*(ALPHA / DIGIT / "-")
     ; IANA registered iCalendar object method

      The "component" parameter conveys the type of iCalendar calendar
      component within the body part.  If the iCalendar object contains
      more than one calendar component type, then multiple component
      parameters MUST be specified.

      The value for the "component" parameter is defined as follows:

     component = "VEVENT"
               / "VTODO"
               / "VJOURNAL"
               / "VFREEBUSY"
               / "VTIMEZONE"
               / x-name
               / iana-token

      The "optinfo" parameter conveys optional information about the
      iCalendar object within the body part.  This parameter can only
      specify semantics already specified by the iCalendar object and
      that can be otherwise determined by parsing the body part.  In
      addition, the optional information specified by this parameter
      MUST be consistent with that information specified by the
      iCalendar object.  For example, it can be used to convey the
      "Attendee" response status to a meeting request.  The parameter
      value consists of a string value.

      The parameter can be specified multiple times.

      This parameter MAY only specify semantics already specified by the
      iCalendar object and that can be otherwise determined by parsing
      the body part.

      The value for the "optinfo" parameter is defined as follows:

     optinfo    = infovalue / qinfovalue

     infovalue  = iana-token / x-name

     qinfovalue = DQUOTE (infovalue) DQUOTE




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   Encoding considerations: This media type can contain 8bit characters,
      so the use of quoted-printable or base64 MIME Content-Transfer-
      Encodings might be necessary when iCalendar objects are
      transferred across protocols restricted to the 7bit repertoire.
      Note that a text valued property in the content entity can also
      have content encoding of special characters using a BACKSLASH
      character (US-ASCII decimal 92) escapement technique.  This means
      that content values can end up encoded twice.

   Security considerations: See Section 8.

   Interoperability considerations: This media type is intended to
      define a common format for conveying calendaring and scheduling
      information between different systems.  It is heavily based on the
      earlier [VCAL] industry specification.

   Published specification: This specification.

   Applications which use this media type: This media type is designed
      for widespread use by Internet calendaring and scheduling
      applications.  In addition, applications in the workflow and
      document management area might find this content-type applicable.
      The iTIP [I-D.ietf-calsify-2446bis], iMIP [I-D.ietf-calsify-
      rfc2447bis] and CalDAV [I-D.dusseault-caldav] Internet protocols
      directly use this media type also.

   Additional information:

      Magic number(s): None.

      File extension(s): The file extension of "ics" is to be used to
         designate a file containing (an arbitrary set of) calendaring
         and scheduling information consistent with this MIME content
         type.

         The file extension of "ifb" is to be used to designate a file
         containing free or busy time information consistent with this
         MIME content type.

      Macintosh file type code(s): The file type code of "iCal" is to be
         used in Apple MacIntosh operating system environments to
         designate a file containing calendaring and scheduling
         information consistent with this MIME media type.

         The file type code of "iFBf" is to be used in Apple MacIntosh
         operating system environments to designate a file containing
         free or busy time information consistent with this MIME media
         type.



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   Person & email address to contact for further information: TBD

   Intended usage: COMMON

   Restrictions on usage: There are no restrictions on where this media
      type can be used.

   Author: TBD

   Change controller: IETF


10.  Acknowledgments

   The editor of this document wish to thank Frank Dawson and Stenerson
   Derik, the original author of RFC2445.

   The editor would also like to thank the Calendaring and Scheduling
   Consortium for advice with this specification, and for organizing
   interoperability testing events to help refine it.


11.  References

11.1.  Normative References

   [I-D.ietf-calsify-2446bis]
              Daboo, C., "iCalendar Transport-Independent
              Interoperability Protocol (iTIP)",
              draft-ietf-calsify-2446bis-01 (work in progress),
              March 2006.

   [I-D.ietf-calsify-rfc2447bis]
              Melnikov, A., "iCalendar Message-Based Interoperability
              Protocol(iMIP)", draft-ietf-calsify-rfc2447bis-02 (work in
              progress), June 2006.

   [ISO.8601.1988]
              International Organization for Standardization, "Data
              elements and interchange formats - Information interchange
              - Representation of dates and times",
              <http://www.w3.org/TR/NOTE-datetime>.

   [ISO.9070.1991]
              International Organization for Standardization,
              "Information Technology_SGML Support Facilities --
              Registration Procedures for Public Text Owner Identifiers,
              Second Edition", April 1991, <http://www.ietf.org/



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              proceedings/98dec/I-D/draft-ietf-calsch-icalfpi-00.txt>.

   [RFC0822]  Crocker, D., "Standard for the format of ARPA Internet
              text messages", STD 11, RFC 822, August 1982.

   [RFC1738]  Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform
              Resource Locators (URL)", RFC 1738, December 1994.

   [RFC1766]  Alvestrand, H., "Tags for the Identification of
              Languages", RFC 1766, March 1995.

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, November 1997.

   [RFC2279]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", RFC 2279, January 1998.

   [RFC2425]  Howes, T., Smith, M., and F. Dawson, "A MIME Content-Type
              for Directory Information", RFC 2425, September 1998.

   [RFC2426]  Dawson, F. and T. Howes, "vCard MIME Directory Profile",
              RFC 2426, September 1998.

   [TZDB]     "Time zone code and data", October 2005,
              <ftp://elsie.nci.nih.gov/pub/>.

   [VCAL]     Internet Mail Consortium, "vCalendar: The Electronic
              Calendaring and Scheduling Exchange Format",
              September 1996, <http://www.imc.org/pdi/vcal-10.txt>.

11.2.  Informative References

   [I-D.dusseault-caldav]
              Dusseault, L., "Calendaring Extensions to WebDAV
              (CalDAV)", draft-dusseault-caldav-12 (work in progress),
              April 2006.




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URIs

   [1]  <mailto:ietf-calsify@osafoundation.org>
















































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Author's Address

   Bernard Desruisseaux (editor)
   Oracle Corporation
   600 blvd. de Maisonneuve West
   Suite 1900
   Montreal, QC  H3A 3J2
   CA

   Email: bernard.desruisseaux@oracle.com
   URI:   http://www.oracle.com/








































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