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Network Working Group                                         F. Dawson
Request for Comments: 2445                                        Lotus
Category: Standards Track                                  D. Stenerson
                                                              Microsoft
                                                          November 1998


     Internet Calendaring and Scheduling Core Object Specification
                              (iCalendar)

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 Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

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.

   This memo is formatted as a registration for a MIME media type per
   [RFC 2048]. 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






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   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) defined in [ITIP] is one such
   scheduling protocol.

Table of Contents

   1 Introduction.....................................................5
   2 Basic Grammar and Conventions....................................6
    2.1 Formatting Conventions .......................................7
    2.2 Related Memos ................................................8
    2.3 International Considerations .................................8
   3 Registration Information.........................................8
    3.1 Content Type .................................................8
    3.2 Parameters ...................................................9
    3.3 Content Header Fields .......................................10
    3.4 Encoding Considerations .....................................10
    3.5 Security Considerations .....................................10
    3.6 Interoperability Considerations .............................11
    3.7 Applications Which Use This Media Type ......................11
    3.8 Additional Information ......................................11
    3.9 Magic Numbers ...............................................11
    3.10 File Extensions ............................................11
    3.11 Contact for Further Information: ...........................12
    3.12 Intended Usage .............................................12
    3.13 Authors/Change Controllers .................................12
   4 iCalendar Object Specification..................................13
    4.1 Content Lines ...............................................13
     4.1.1 List and Field Separators ................................16
     4.1.2 Multiple Values ..........................................16
     4.1.3 Binary Content ...........................................16



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     4.1.4 Character Set ............................................17
    4.2 Property Parameters .........................................17
     4.2.1 Alternate Text Representation ............................18
     4.2.2 Common Name ..............................................19
     4.2.3 Calendar User Type .......................................20
     4.2.4 Delegators ...............................................20
     4.2.5 Delegatees ...............................................21
     4.2.6 Directory Entry Reference ................................21
     4.2.7 Inline Encoding ..........................................22
     4.2.8 Format Type ..............................................23
     4.2.9 Free/Busy Time Type ......................................23
     4.2.10 Language ................................................24
     4.2.11 Group or List Membership ................................25
     4.2.12 Participation Status ....................................25
     4.2.13 Recurrence Identifier Range .............................27
     4.2.14 Alarm Trigger Relationship ..............................27
     4.2.15 Relationship Type .......................................28
     4.2.16 Participation Role ......................................29
     4.2.17 RSVP Expectation ........................................29
     4.2.18 Sent By .................................................30
     4.2.19 Time Zone Identifier ....................................30
     4.2.20 Value Data Types ........................................32
    4.3 Property Value Data Types ...................................32
     4.3.1 Binary ...................................................33
     4.3.2 Boolean ..................................................33
     4.3.3 Calendar User Address ....................................34
     4.3.4 Date .....................................................34
     4.3.5 Date-Time ................................................35
     4.3.6 Duration .................................................37
     4.3.7 Float ....................................................38
     4.3.8 Integer ..................................................38
     4.3.9 Period of Time ...........................................39
     4.3.10 Recurrence Rule .........................................40
     4.3.11 Text ....................................................45
     4.3.12 Time ....................................................47
     4.3.13 URI .....................................................49
     4.3.14 UTC Offset ..............................................49
    4.4 iCalendar Object ............................................50
    4.5 Property ....................................................51
    4.6 Calendar Components .........................................51
     4.6.1 Event Component ..........................................52
     4.6.2 To-do Component ..........................................55
     4.6.3 Journal Component ........................................56
     4.6.4 Free/Busy Component ......................................58
     4.6.5 Time Zone Component ......................................60
     4.6.6 Alarm Component ..........................................67
    4.7 Calendar Properties .........................................73
     4.7.1 Calendar Scale ...........................................73



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     4.7.2 Method ...................................................74
     4.7.3 Product Identifier .......................................75
     4.7.4 Version ..................................................76
    4.8 Component Properties ........................................77
     4.8.1 Descriptive Component Properties .........................77
       4.8.1.1 Attachment ...........................................77
       4.8.1.2 Categories ...........................................78
       4.8.1.3 Classification .......................................79
       4.8.1.4 Comment ..............................................80
       4.8.1.5 Description ..........................................81
       4.8.1.6 Geographic Position ..................................82
       4.8.1.7 Location .............................................84
       4.8.1.8 Percent Complete .....................................85
       4.8.1.9 Priority .............................................85
       4.8.1.10 Resources ...........................................87
       4.8.1.11 Status ..............................................88
       4.8.1.12 Summary .............................................89
     4.8.2 Date and Time Component Properties .......................90
       4.8.2.1 Date/Time Completed ..................................90
       4.8.2.2 Date/Time End ........................................91
       4.8.2.3 Date/Time Due ........................................92
       4.8.2.4 Date/Time Start ......................................93
       4.8.2.5 Duration .............................................94
       4.8.2.6 Free/Busy Time .......................................95
       4.8.2.7 Time Transparency ....................................96
     4.8.3 Time Zone Component Properties ...........................97
       4.8.3.1 Time Zone Identifier .................................97
       4.8.3.2 Time Zone Name .......................................98
       4.8.3.3 Time Zone Offset From ................................99
       4.8.3.4 Time Zone Offset To .................................100
       4.8.3.5 Time Zone URL .......................................101
     4.8.4 Relationship Component Properties .......................102
       4.8.4.1 Attendee ............................................102
       4.8.4.2 Contact .............................................104
       4.8.4.3 Organizer ...........................................106
       4.8.4.4 Recurrence ID .......................................107
       4.8.4.5 Related To ..........................................109
       4.8.4.6 Uniform Resource Locator ............................110
       4.8.4.7 Unique Identifier ...................................111
     4.8.5 Recurrence Component Properties .........................112
       4.8.5.1 Exception Date/Times ................................112
       4.8.5.2 Exception Rule ......................................114
       4.8.5.3 Recurrence Date/Times ...............................115
       4.8.5.4 Recurrence Rule .....................................117
     4.8.6 Alarm Component Properties ..............................126
       4.8.6.1 Action ..............................................126
       4.8.6.2 Repeat Count ........................................126
       4.8.6.3 Trigger .............................................127



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     4.8.7 Change Management Component Properties ..................129
       4.8.7.1 Date/Time Created ...................................129
       4.8.7.2 Date/Time Stamp .....................................130
       4.8.7.3 Last Modified .......................................131
       4.8.7.4 Sequence Number .....................................131
     4.8.8 Miscellaneous Component Properties ......................133
       4.8.8.1 Non-standard Properties .............................133
       4.8.8.2 Request Status ......................................134
   5 iCalendar Object Examples......................................136
   6 Recommended Practices..........................................140
   7 Registration of Content Type Elements..........................141
    7.1 Registration of New and Modified iCalendar Object Methods ..141
    7.2 Registration of New Properties .............................141
     7.2.1 Define the property .....................................142
     7.2.2 Post the Property definition ............................143
     7.2.3 Allow a comment period ..................................143
     7.2.4 Submit the property for approval ........................143
    7.3 Property Change Control ....................................143
   8 References.....................................................144
   9 Acknowledgments................................................145
   10 Authors' and Chairs' Addresses................................146
   11 Full Copyright Statement......................................148

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



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   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 [ITIP].

   The memo also includes a formal grammar for the content type based on
   the Internet ABNF defined in [RFC 2234]. 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
   "OPTIONAL" in this document are to be interoperated as described in
   [RFC 2119].

   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 [RFC 2234].
   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 and hexadecimal 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.




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   The format for the iCalendar object is based on the syntax of the
   [RFC 2425] content type. While the iCalendar object is not a profile
   of the [RFC 2425] content type, it does reuse a number of the
   elements from the [RFC 2425] 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 [ITIP] 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 [ITIP].
   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] are referred to with
   capitalized, quoted-strings of text. For example, "REQUEST" refers to
   the method for requesting a scheduling calendar component be created
   or modified, "REPLY" refers to the method a recipient of a request
   uses to update their status with the "Organizer" of the calendar
   component.

   The properties defined by this memo are referred to with capitalized,
   quoted-strings of text, followed by the word "property". For example,
   "ATTENDEE" property refers to the iCalendar property used to convey
   the calendar address of a calendar user. Property parameters defined
   by this memo are referred to with lowercase, quoted-strings of text,
   followed by the word "parameter". For example, "value" parameter
   refers to the iCalendar property parameter used to override the
   default 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.











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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, [ICAL], specifies a core
   specification of objects, data types, properties and property
   parameters.

   [ITIP] - specifies an interoperability protocol for scheduling
   between different implementations;

   [IMIP] specifies an Internet email binding for [ITIP].

   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.

3  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.

3.1 Content Type

   The following text is intended to register this memo as the MIME
   content type "text/calendar".

     To: ietf-hide@address.com

     Subject: Registration of MIME content type text/calendar.

     MIME media type name: text

     MIME subtype name: calendar



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3.2 Parameters

   Required parameters: none

   Optional parameters: charset, method, component and optinfo

   The "charset" parameter is defined in [RFC 2046] 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
   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.



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   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

3.3 Content Header Fields

   Optional content header fields: Any header fields defined by [RFC
   2045].

3.4 Encoding Considerations

   This MIME content 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.

3.5 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".






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   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
   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.

3.6 Interoperability Considerations

   This MIME content 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.

3.7 Applications Which Use This Media Type

   This content-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] and [IMIP] Internet protocols directly
   use this content-type also. Future work on an Internet calendar
   access protocol will utilize this content-type too.

3.8 Additional Information

   This memo defines this content-type.

3.9 Magic Numbers

   None.

3.10 File Extensions

   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.






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   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 codes: 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.

3.11 Contact for Further Information:

   Frank Dawson
   6544 Battleford Drive
   Raleigh, NC 27613-3502
   919-676-9515 (Telephone)
   919-676-9564 (Data/Facsimile)
   hide@address.com (Internet Mail)

   Derik Stenerson
   One Microsoft Way
   Redmond, WA  98052-6399
   425-936-5522 (Telephone)
   425-936-7329 (Facsimile)
   hide@address.com (Internet Mail)

3.12 Intended Usage

   COMMON

3.13 Authors/Change Controllers

   Frank Dawson
   6544 Battleford Drive
   Raleigh, NC 27613-3502
   919-676-9515 (Telephone)
   919-676-9564 (Data/Facsimile)
   hide@address.com (Internet Mail)

   Derik Stenerson
   One Microsoft Way
   Redmond, WA  98052-6399
   425-936-5522 (Telephone)
   425-936-7329 (Facsimile)
   hide@address.com (Internet Mail)



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4 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.

4.1 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.






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   The content information associated with an iCalendar object is
   formatted using a syntax similar to that defined by [RFC 2425]. 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 / "-")
     ; Reservered for experimental use. Not intended for use in
     ; released products.

     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)



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







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4.1.1 List and Field Separators

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

   Some property values are defined in terms of multiple parts. These
   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:
      hide@address.com

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

4.1.2 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.

4.1.3 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



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   can be included within an iCalendar object, but only after first
   encoding it into text using the "BASE64" encoding method defined in
   [RFC 2045]. Inline binary contact 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://xyz.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...>

4.1.4 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 [RFC 2279].

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

4.2 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 DOUBLE-QUOTE (US-ASCII
   decimal 22) character. The DOUBLE-QUOTE (US-ASCII decimal 22)
   character is used as a delimiter for parameter values that contain
   restricted characters or URI text. For example:




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

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

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

     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)

4.2.1 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:




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     altrepparam        = "ALTREP" "=" DQUOTE uri DQUOTE

   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:<hide@address.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:<hide@address.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>

4.2.2 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.







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   Example:

     ORGANIZER;CN="John Smith":MAILTO:hide@address.com

4.2.3 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-hide@address.com

4.2.4 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)





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   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 uses that have delegated their participation in a
   group scheduled event or to-do to the calendar user specified by the
   property. The value MUST be a MAILTO URI as defined in [RFC 1738].
   The individual calendar address parameter values MUST each be
   specified in a quoted-string.

   Example:

     ATTENDEE;DELEGATED-FROM="MAILTO:hide@address.com":MAILTO:
      hide@address.com

4.2.5 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 [RFC 1738]. The individual calendar
   address parameter values MUST each be specified in a quoted-string.

   Example:

     ATTENDEE;DELEGATED-TO="MAILTO:hide@address.com","MAILTO:jqpublic@
      host.com":MAILTO:hide@address.com

4.2.6 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:



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     dirparam   = "DIR" "=" DQUOTE uri DQUOTE

   Description: This parameter can be specified on properties with a
   CAL-ADDRESS value type. The parameter specifies a reference to the
   directory entry associated with the calendar user specified by the
   property. The parameter value is a URI. The 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:hide@address.com

4.2.7 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 [RFC 2045]
                        / "BASE64"
        ; "BASE64" binary encoding format is defined in [RFC 2045]
                        / 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 [RFC 2045].

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









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   Example:

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

4.2.8 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/binary:ftp://domain.com/pub/docs/
       agenda.doc

4.2.9 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)



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        ; Some other IANA registered iCalendar data type.

   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

4.2.10 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 [RFC 1766]>

   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 [RFC 1766].

   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





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   The following example makes use of the Quoted-Printable encoding in
   order to represent non-ASCII characters.

     LOCATION;LANGUAGE=da:K=F8benhavn
     LOCATION;LANGUAGE=en:Copenhagen

4.2.11  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-hide@address.com":MAILTO:hide@address.com

     ATTENDEE;MEMBER="MAILTO:hide@address.com","MAILTO:hide@address.com
      com":MAILTO:hide@address.com

4.2.12 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:

     partstatparam      = "PARTSTAT" "="
                         ("NEEDS-ACTION"        ; Event needs action
                        / "ACCEPTED"            ; Event accepted
                        / "DECLINED"            ; Event declined



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                        / "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.

   Example:

     ATTENDEE;PARTSTAT=DECLINED:MAILTO:hide@address.com



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4.2.13  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

4.2.14 Alarm Trigger Relationship

   Parameter Name: RELATED

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

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

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




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   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

4.2.15 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 allowable
   property, the default relationship type is PARENT.

   Example:

     RELATED-TO;RELTYPE=SIBLING:<19960401-080045-hide@address.com>





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4.2.16 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:hide@address.com

4.2.17  RSVP Expectation

   Parameter Name: RSVP

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

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

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





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

   Example:

     ATTENDEE;RSVP=TRUE:MAILTO:hide@address.com

4.2.18  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 [RFC
   1738]. The individual calendar address parameter values MUST each be
   specified in a quoted-string.

   Example:

     ORGANIZER;SENT-BY:"MAILTO:hide@address.com":MAILTO:hide@address.com

4.2.19 Time Zone Identifier

   Parameter Name: TZID

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

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

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

     tzidprefix = "/"



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   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 [TZ]. 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 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.








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4.2.20 Value Data Types

   Parameter Name: VALUE

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

   Format Definition: The "VALUE" 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.

   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.

4.3 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"



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   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.

4.3.1   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.

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

     binary     = *(4b-char) [b-end]
     ; A "BASE64" encoded character string, as defined by [RFC 2045].

     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 [RFC 2045]. 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
        <...remainder of "BASE64" encoded binary data...>

4.3.2   Boolean

   Value Name: BOOLEAN

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

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




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     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

4.3.3   Calendar User Address

   Value Name: CAL-ADDRESS

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

   Formal Definition: The value type is as defined by the following
   notation:

     cal-address        = uri

   Description: The value is a URI as defined by [RFC 1738] 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 [RFC 1738]. No additional content value
   encoding (i.e., BACKSLASH character encoding) is defined for this
   value type.

   Example:

     ATTENDEE:MAILTO:hide@address.com

4.3.4 Date

   Value Name: DATE

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

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

     date               = date-value

     date-value         = date-fullyear date-month date-mday
     date-fullyear      = 4DIGIT



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     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] 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

4.3.5   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.

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

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

   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] 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:



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     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.

   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





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   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

4.3.6   Duration

   Value Name: DURATION

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

   Formal 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] basic format for
   the duration of time. The format can represent durations in terms of
   weeks, days, hours, minutes, and seconds.




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   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

4.3.7   Float

   Value Name: FLOAT

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

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

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

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

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

   Example:

     1000000.0000001
     1.333
     -3.14

4.3.8 Integer

     Value Name:INTEGER

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

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

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




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     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

4.3.9 Period of Time

   Value Name: PERIOD

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

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

     period     = period-explicit / period-start

     period-explicit = date-time "/" date-time
     ; [ISO 8601] 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] 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] 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]
   complete representation, basic format for the "DATE-TIME" start of



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   the period, followed by a SOLIDUS character (US-ASCII decimal 47),
   followed by the [ISO 8601] 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.

4.3.10 Recurrence Rule

   Value Name: RECUR

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

   Formal 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 )              /



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                ( ";" 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

     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) )



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     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). 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



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   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.

   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]. 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.



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

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

   The BYSETPOS rule part specifies a COMMA character (US-ASCII decimal
   44) separated list of values which corresponds to the nth occurrence
   within the set of 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.



Dawson & Stenerson          Standards Track                    [Page 44]

RFC 2445                       iCalendar                   November 1998


   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

   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