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RFC 5545

Internet Calendaring and Scheduling Core Object Specification (iCalendar)

Pages: 168
Proposed Standard
Errata
Obsoletes:  2445
Updated by:  55466868752979537986
Part 1 of 7 – Pages 1 to 13
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Network Working Group                               B. Desruisseaux, Ed.
Request for Comments: 5545                                        Oracle
Obsoletes: 2445                                           September 2009
Category: Standards Track


     Internet Calendaring and Scheduling Core Object Specification
                              (iCalendar)

Abstract

This document defines the iCalendar data format for representing and exchanging calendaring and scheduling information such as events, to-dos, journal entries, and free/busy information, independent of any particular calendar service or protocol. Status of This Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright and License Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format
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   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Basic Grammar and Conventions . . . . . . . . . . . . . . . . 6 2.1. Formatting Conventions . . . . . . . . . . . . . . . . . 6 2.2. Related Memos . . . . . . . . . . . . . . . . . . . . . . 7 3. iCalendar Object Specification . . . . . . . . . . . . . . . 8 3.1. Content Lines . . . . . . . . . . . . . . . . . . . . . . 8 3.1.1. List and Field Separators . . . . . . . . . . . . . . 11 3.1.2. Multiple Values . . . . . . . . . . . . . . . . . . . 11 3.1.3. Binary Content . . . . . . . . . . . . . . . . . . . 11 3.1.4. Character Set . . . . . . . . . . . . . . . . . . . . 12 3.2. Property Parameters . . . . . . . . . . . . . . . . . . . 12 3.2.1. Alternate Text Representation . . . . . . . . . . . . 13 3.2.2. Common Name . . . . . . . . . . . . . . . . . . . . . 15 3.2.3. Calendar User Type . . . . . . . . . . . . . . . . . 15 3.2.4. Delegators . . . . . . . . . . . . . . . . . . . . . 16 3.2.5. Delegatees . . . . . . . . . . . . . . . . . . . . . 16 3.2.6. Directory Entry Reference . . . . . . . . . . . . . . 17 3.2.7. Inline Encoding . . . . . . . . . . . . . . . . . . . 17 3.2.8. Format Type . . . . . . . . . . . . . . . . . . . . . 18 3.2.9. Free/Busy Time Type . . . . . . . . . . . . . . . . . 19 3.2.10. Language . . . . . . . . . . . . . . . . . . . . . . 20 3.2.11. Group or List Membership . . . . . . . . . . . . . . 20 3.2.12. Participation Status . . . . . . . . . . . . . . . . 21 3.2.13. Recurrence Identifier Range . . . . . . . . . . . . . 22 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 . . . . . . . . . . . . . . . . . . . . . . . . 35 3.3.8. Integer . . . . . . . . . . . . . . . . . . . . . . . 35 3.3.9. Period of Time . . . . . . . . . . . . . . . . . . . 36 3.3.10. Recurrence Rule . . . . . . . . . . . . . . . . . . . 37 3.3.11. Text . . . . . . . . . . . . . . . . . . . . . . . . 45
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       3.3.12. Time  . . . . . . . . . . . . . . . . . . . . . . . .  47
       3.3.13. URI . . . . . . . . . . . . . . . . . . . . . . . . .  49
       3.3.14. UTC Offset  . . . . . . . . . . . . . . . . . . . . .  49
     3.4.  iCalendar Object  . . . . . . . . . . . . . . . . . . . .  50
     3.5.  Property  . . . . . . . . . . . . . . . . . . . . . . . .  51
     3.6.  Calendar Components . . . . . . . . . . . . . . . . . . .  51
       3.6.1.  Event Component . . . . . . . . . . . . . . . . . . .  52
       3.6.2.  To-Do Component . . . . . . . . . . . . . . . . . . .  55
       3.6.3.  Journal Component . . . . . . . . . . . . . . . . . .  57
       3.6.4.  Free/Busy Component . . . . . . . . . . . . . . . . .  59
       3.6.5.  Time Zone Component . . . . . . . . . . . . . . . . .  62
       3.6.6.  Alarm Component . . . . . . . . . . . . . . . . . . .  71
     3.7.  Calendar Properties . . . . . . . . . . . . . . . . . . .  76
       3.7.1.  Calendar Scale  . . . . . . . . . . . . . . . . . . .  76
       3.7.2.  Method  . . . . . . . . . . . . . . . . . . . . . . .  77
       3.7.3.  Product Identifier  . . . . . . . . . . . . . . . . .  78
       3.7.4.  Version . . . . . . . . . . . . . . . . . . . . . . .  79
     3.8.  Component Properties  . . . . . . . . . . . . . . . . . .  80
       3.8.1.  Descriptive Component Properties  . . . . . . . . . .  80
         3.8.1.1.  Attachment  . . . . . . . . . . . . . . . . . . .  80
         3.8.1.2.  Categories  . . . . . . . . . . . . . . . . . . .  81
         3.8.1.3.  Classification  . . . . . . . . . . . . . . . . .  82
         3.8.1.4.  Comment . . . . . . . . . . . . . . . . . . . . .  83
         3.8.1.5.  Description . . . . . . . . . . . . . . . . . . .  84
         3.8.1.6.  Geographic Position . . . . . . . . . . . . . . .  85
         3.8.1.7.  Location  . . . . . . . . . . . . . . . . . . . .  87
         3.8.1.8.  Percent Complete  . . . . . . . . . . . . . . . .  88
         3.8.1.9.  Priority  . . . . . . . . . . . . . . . . . . . .  89
         3.8.1.10. Resources . . . . . . . . . . . . . . . . . . . .  91
         3.8.1.11. Status  . . . . . . . . . . . . . . . . . . . . .  92
         3.8.1.12. Summary . . . . . . . . . . . . . . . . . . . . .  93
       3.8.2.  Date and Time Component Properties  . . . . . . . . .  94
         3.8.2.1.  Date-Time Completed . . . . . . . . . . . . . . .  94
         3.8.2.2.  Date-Time End . . . . . . . . . . . . . . . . . .  95
         3.8.2.3.  Date-Time Due . . . . . . . . . . . . . . . . . .  96
         3.8.2.4.  Date-Time Start . . . . . . . . . . . . . . . . .  97
         3.8.2.5.  Duration  . . . . . . . . . . . . . . . . . . . .  99
         3.8.2.6.  Free/Busy Time  . . . . . . . . . . . . . . . . . 100
         3.8.2.7.  Time Transparency . . . . . . . . . . . . . . . . 101
       3.8.3.  Time Zone Component Properties  . . . . . . . . . . . 102
         3.8.3.1.  Time Zone Identifier  . . . . . . . . . . . . . . 102
         3.8.3.2.  Time Zone Name  . . . . . . . . . . . . . . . . . 103
         3.8.3.3.  Time Zone Offset From . . . . . . . . . . . . . . 104
         3.8.3.4.  Time Zone Offset To . . . . . . . . . . . . . . . 105
         3.8.3.5.  Time Zone URL . . . . . . . . . . . . . . . . . . 106
       3.8.4.  Relationship Component Properties . . . . . . . . . . 106
         3.8.4.1.  Attendee  . . . . . . . . . . . . . . . . . . . . 107
         3.8.4.2.  Contact . . . . . . . . . . . . . . . . . . . . . 109
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         3.8.4.3.  Organizer . . . . . . . . . . . . . . . . . . . . 111
         3.8.4.4.  Recurrence ID . . . . . . . . . . . . . . . . . . 112
         3.8.4.5.  Related To  . . . . . . . . . . . . . . . . . . . 115
         3.8.4.6.  Uniform Resource Locator  . . . . . . . . . . . . 116
         3.8.4.7.  Unique Identifier . . . . . . . . . . . . . . . . 117
       3.8.5.  Recurrence Component Properties . . . . . . . . . . . 118
         3.8.5.1.  Exception Date-Times  . . . . . . . . . . . . . . 118
         3.8.5.2.  Recurrence Date-Times . . . . . . . . . . . . . . 120
         3.8.5.3.  Recurrence Rule . . . . . . . . . . . . . . . . . 122
       3.8.6.  Alarm Component Properties  . . . . . . . . . . . . . 132
         3.8.6.1.  Action  . . . . . . . . . . . . . . . . . . . . . 132
         3.8.6.2.  Repeat Count  . . . . . . . . . . . . . . . . . . 133
         3.8.6.3.  Trigger . . . . . . . . . . . . . . . . . . . . . 133
       3.8.7.  Change Management Component Properties  . . . . . . . 136
         3.8.7.1.  Date-Time Created . . . . . . . . . . . . . . . . 136
         3.8.7.2.  Date-Time Stamp . . . . . . . . . . . . . . . . . 137
         3.8.7.3.  Last Modified . . . . . . . . . . . . . . . . . . 138
         3.8.7.4.  Sequence Number . . . . . . . . . . . . . . . . . 138
       3.8.8.  Miscellaneous Component Properties  . . . . . . . . . 139
         3.8.8.1.  IANA Properties . . . . . . . . . . . . . . . . . 140
         3.8.8.2.  Non-Standard Properties . . . . . . . . . . . . . 140
         3.8.8.3.  Request Status  . . . . . . . . . . . . . . . . . 141
   4.  iCalendar Object Examples . . . . . . . . . . . . . . . . . . 144
   5.  Recommended Practices . . . . . . . . . . . . . . . . . . . . 147
   6.  Internationalization Considerations . . . . . . . . . . . . . 148
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . 148
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 149
     8.1.  iCalendar Media Type Registration . . . . . . . . . . . . 149
     8.2.  New iCalendar Elements Registration . . . . . . . . . . . 152
       8.2.1.  iCalendar Elements Registration Procedure . . . . . . 152
       8.2.2.  Registration Template for Components  . . . . . . . . 152
       8.2.3.  Registration Template for Properties  . . . . . . . . 153
       8.2.4.  Registration Template for Parameters  . . . . . . . . 153
       8.2.5.  Registration Template for Value Data Types  . . . . . 154
       8.2.6.  Registration Template for Values  . . . . . . . . . . 154
     8.3.  Initial iCalendar Elements Registries . . . . . . . . . . 155
       8.3.1.  Components Registry . . . . . . . . . . . . . . . . . 155
       8.3.2.  Properties Registry . . . . . . . . . . . . . . . . . 156
       8.3.3.  Parameters Registry . . . . . . . . . . . . . . . . . 158
       8.3.4.  Value Data Types Registry . . . . . . . . . . . . . . 159
       8.3.5.  Calendar User Types Registry  . . . . . . . . . . . . 160
       8.3.6.  Free/Busy Time Types Registry . . . . . . . . . . . . 160
       8.3.7.  Participation Statuses Registry . . . . . . . . . . . 161
       8.3.8.  Relationship Types Registry . . . . . . . . . . . . . 161
       8.3.9.  Participation Roles Registry  . . . . . . . . . . . . 162
       8.3.10. Actions Registry  . . . . . . . . . . . . . . . . . . 162
       8.3.11. Classifications Registry  . . . . . . . . . . . . . . 162
       8.3.12. Methods Registry  . . . . . . . . . . . . . . . . . . 163
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   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 163
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . 164
     10.1. Normative References  . . . . . . . . . . . . . . . . . . 164
     10.2. Informative References  . . . . . . . . . . . . . . . . . 165
   Appendix A.  Differences from RFC 2445  . . . . . . . . . . . . . 167
     A.1.  New Restrictions  . . . . . . . . . . . . . . . . . . . . 167
     A.2.  Restrictions Removed  . . . . . . . . . . . . . . . . . . 167
     A.3.  Deprecated Features . . . . . . . . . . . . . . . . . . . 167

1. Introduction

The use of calendaring and scheduling has grown considerably in the last decade. Enterprise and inter-enterprise business has become dependent on rapid scheduling of events and actions using this information technology. This memo is intended to progress the level of interoperability possible between dissimilar calendaring and scheduling applications. This memo defines a MIME content type for exchanging electronic calendaring and scheduling information. The Internet Calendaring and Scheduling Core Object Specification, or iCalendar, allows for the capture and exchange of information normally stored within a calendaring and scheduling application; such as a Personal Information Manager (PIM) or a Group-Scheduling product. The iCalendar format is suitable as an exchange format between applications or systems. The format is defined in terms of a MIME content type. This will enable the object to be exchanged using several transports, including but not limited to SMTP, HTTP, a file system, desktop interactive protocols such as the use of a memory- based clipboard or drag/drop interactions, point-to-point asynchronous communication, wired-network transport, or some form of unwired transport such as infrared. 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 as 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 [2446bis]. The memo also includes a formal grammar for the content type based on the Internet ABNF defined in [RFC5234]. This ABNF is required for the implementation of parsers and to serve as the definitive reference when ambiguities or questions arise in interpreting the descriptive prose definition of the memo. Additional restrictions
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   that could not easily be expressed with the ABNF syntax are specified
   as comments in the ABNF.  Comments with normative statements should
   be treated as such.

2. Basic Grammar and Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. This memo makes use of both a descriptive prose and a more formal notation for defining the calendaring and scheduling format. The notation used in this memo is the ABNF notation of [RFC5234]. Readers intending on implementing the format defined in this memo should be familiar with this notation in order to properly interpret the specifications of this memo. All numeric values used in this memo are given in decimal notation. All names of properties, property parameters, enumerated property values, and property parameter values are case-insensitive. However, all other property values are case-sensitive, unless otherwise stated. Note: All indented editorial notes, such as this one, are intended to provide the reader with additional information. The information is not essential to the building of an implementation conformant with this memo. The information is provided to highlight a particular feature or characteristic of the memo. The format for the iCalendar object is based on the syntax of the text/directory media type [RFC2425]. While the iCalendar object is not a profile of the text/directory media type [RFC2425], it does reuse a number of the elements from the [RFC2425] specification.

2.1. Formatting Conventions

The elements defined in this memo are defined in prose. Many of the terms used to describe these have common usage that is different than the standards usage of this memo. In order to reference, within this memo, elements of the calendaring and scheduling model, core object (this memo), or interoperability protocol [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 uppercase. For example, "Organizer" refers to a role of a "Calendar User" within the scheduling protocol defined by [2446bis]. Calendar components defined by this memo are referred to
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   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 [2446bis] are referred to with
   capitalized, quoted-strings of text.  For example, "REQUEST" refers
   to the method for requesting a scheduling calendar component be
   created or modified, and "REPLY" refers to the method a recipient of
   a request uses to update their status with the "Organizer" of the
   calendar component.

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

   The following table lists the different characters from the
   [US-ASCII] character set that is referenced in this document.  For
   each character, the table specifies the character name used
   throughout this document, along with its US-ASCII decimal codepoint.
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              +------------------------+-------------------+
              | Character name         | Decimal codepoint |
              +------------------------+-------------------+
              | HTAB                   | 9                 |
              | LF                     | 10                |
              | CR                     | 13                |
              | DQUOTE                 | 22                |
              | SPACE                  | 32                |
              | PLUS SIGN              | 43                |
              | COMMA                  | 44                |
              | HYPHEN-MINUS           | 45                |
              | PERIOD                 | 46                |
              | SOLIDUS                | 47                |
              | COLON                  | 58                |
              | SEMICOLON              | 59                |
              | LATIN CAPITAL LETTER N | 78                |
              | LATIN CAPITAL LETTER T | 84                |
              | LATIN CAPITAL LETTER X | 88                |
              | LATIN CAPITAL LETTER Z | 90                |
              | BACKSLASH              | 92                |
              | LATIN SMALL LETTER N   | 110               |
              +------------------------+-------------------+

2.2. Related Memos

Implementers will need to be familiar with several other memos that, along with this memo, form a framework for Internet calendaring and scheduling standards. This memo specifies a core specification of objects, value types, properties, and property parameters. o iTIP [2446bis] specifies an interoperability protocol for scheduling between different implementations; o iCalendar Message-Based Interoperability Protocol (iMIP) [2447bis] specifies an Internet email binding for [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.

3. iCalendar Object Specification

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

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

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

3.1. Content Lines

The iCalendar object is organized into individual lines of text, called content lines. Content lines are delimited by a line break, which is a CRLF sequence (CR character followed by LF character). 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 or HTAB). 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 and the linear white-space character that immediately follows.
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   When parsing a content line, folded lines MUST first be unfolded
   according to the unfolding procedure described above.

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

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

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

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

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

     name          = iana-token / x-name

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

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

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

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

     param-name    = iana-token / x-name

     param-value   = paramtext / quoted-string

     paramtext     = *SAFE-CHAR
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     value         = *VALUE-CHAR

     quoted-string = DQUOTE *QSAFE-CHAR DQUOTE

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

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

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

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

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

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

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

3.1.1. List and Field Separators

Some properties and parameters allow a list of values. Values in a list of values MUST be separated by a COMMA character. 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. Some property values are defined in terms of multiple parts. These structured property values MUST have their value parts separated by a SEMICOLON character. Some properties allow a list of parameters. Each property parameter in a list of property parameters MUST be separated by a SEMICOLON character.
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   Property parameters with values containing a COLON character, a
   SEMICOLON character 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 character is
   used to separate property values in a value list.

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

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

3.1.2. Multiple Values

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

3.1.3. Binary Content

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

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

3.1.4. Character Set

There is not a property parameter to declare the charset used in a property value. The default charset for an iCalendar stream is UTF-8 as defined in [RFC3629]. The "charset" Content-Type parameter MUST be used in MIME transports to specify the charset being used.


(page 13 continued on part 2)

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