RFC 2445 (RFC2445)

RFC 2445 - Internet Calendaring and Scheduling Core Object Specification (iCalendar)


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
   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
     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
     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

     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
   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.

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.

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-types@uninett.no

     Subject: Registration of MIME content type text/calendar.

     MIME media type name: text

     MIME subtype name: calendar

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.
   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".

   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.

   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) Frank_Dawson@Lotus.com (Internet Mail)

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

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

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.
   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)

     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.

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:
      jsmith@host.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

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

The "ALTREP" property parameter value might point to a "text/html" content portion.
     Content-Type:text/html
     Content-Id:<part3.msg.970415T083000@host.com>

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

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.
   Example:
     ORGANIZER;CN="John Smith":MAILTO:jsmith@host.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-calsch@imc.org

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)

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:jsmith@host.com":MAILTO:
      jdoe@host.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:jdoe@host.com","MAILTO:jqpublic@
      host.com":MAILTO:jsmith@host.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:
     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:jimdo@host1.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".
   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)

        ; 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

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-calsch@imc.org":MAILTO:jsmith@host.com

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

                        / "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:jsmith@host.com

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

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:<19960401-080045-4000F192713@host.com>

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:mrbig@host.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

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

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:sray@host.com":MAILTO:jsmith@host.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 = "/"

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.

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"

   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:
     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:jane_doe@host.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

     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:
     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
   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.
   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

     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
   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 )              /

                ( ";" 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) )

     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
   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.

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.
   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 January at 8 AM and 9 AM, every other year". Then, "BYMINUTE=30" would be applied to arrive at "every Sunday in January at 8:30 AM and 9:30 AM, every other year". Then, lacking information from RRULE, the second is derived from DTSTART, to end up in "every Sunday in January at 8:30:00 AM and 9:30:00 AM, every other year". Similarly, if the BYMINUTE, BYHOUR, BYDAY, BYMONTHDAY or BYMONTH rule part were missing, the appropriate minute, hour, day or month would have been retrieved from the "DTSTART" property.
   No additional content value encoding (i.e., BACKSLASH character
   encoding) is defined for this value type.
   Example: The following is a rule which specifies 10 meetings which
   occur every other day:
     FREQ=DAILY;COUNT=10;INTERVAL=2

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

4.3.11 Text

Value Name: TEXT

   Purpose This value type is used to identify values that contain human
   readable text.
   Formal Definition: The character sets supported by this revision of
   iCalendar are UTF-8 and US ASCII thereof. The applicability to other
   character sets is for future work. The value type is defined by the
   following notation.
     text       = *(TSAFE-CHAR / ":" / DQUOTE / ESCAPED-CHAR)
     ; Folded according to description above

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

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

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

Description: If the property permits, multiple "text" values are specified by a COMMA character (US-ASCII decimal 44) separated list of values.
   The language in which the text is represented can be controlled by
   the "LANGUAGE" property parameter.
   An intentional formatted text line break MUST only be included in a
   "TEXT" property value by representing the line break with the
   character sequence of BACKSLASH (US-ASCII decimal 92), followed by a
   LATIN SMALL LETTER N (US-ASCII decimal 110) or a LATIN CAPITAL LETTER
   N (US-ASCII decimal 78), that is "\n" or "\N".
   The "TEXT" property values may also contain special characters that
   are used to signify delimiters, such as a COMMA character for lists
   of values or a SEMICOLON character for structured values. In order to
   support the inclusion of these special characters in "TEXT" property
   values, they MUST be escaped with a BACKSLASH character. A BACKSLASH
   character (US-ASCII decimal 92) in a "TEXT" property value MUST be
   escaped with another BACKSLASH character. A COMMA character in a
   "TEXT" property value MUST be escaped with a BACKSLASH character
   (US-ASCII decimal 92). A SEMICOLON character in a "TEXT" property
   value MUST be escaped with a BACKSLASH character (US-ASCII decimal
   92).  However, a COLON character in a "TEXT" property value SHALL NOT
   be escaped with a BACKSLASH character.Example: A multiple line value
   of:
     Project XYZ Final Review
     Conference Room - 3B
     Come Prepared.

would be represented as:
     Project XYZ Final Review\nConference Room - 3B\nCome Prepared.

4.3.12 Time

Value Name: TIME

   Purpose: This value type is used to identify values that contain a
   time of day.
   Formal Definition: The data type is defined by the following
   notation:
     time               = time-hour time-minute time-second [time-utc]

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

     time-utc   = "Z"

Description: If the property permits, multiple "time" values are specified by a COMMA character (US-ASCII decimal 44) separated list of values. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type.
   The "TIME" data type is used to identify values that contain a time
   of day. The format is based on the [ISO 8601] complete
   representation, basic format for a time of day. The text format
   consists of a two-digit 24-hour of the day (i.e., values 0-23), two-
   digit minute in the hour (i.e., values 0-59), and two-digit seconds
   in the minute (i.e., values 0-60). The seconds value of 60 MUST only
   to be used to account for "leap" seconds. Fractions of a second are
   not supported by this format.
   In parallel to the "DATE-TIME" definition above, the "TIME" data type
   expresses time values in three forms:
   The form of time with UTC offset MUST NOT be used. For example, the
   following is NOT VALID for a time value:
     230000-0800        ;Invalid time format

FORM #1 LOCAL TIME
   The local time form is simply a time value that does not contain the
   UTC designator nor does it reference a time zone. For example, 11:00
   PM:
     230000

Time values of this type are said to be "floating" and are not bound to any time zone in particular. They are used to represent the same hour, minute, and second value regardless of which time zone is currently being observed. For example, an event can be defined that indicates that an individual will be busy from 11:00 AM to 1:00 PM every day, no matter which time zone the person is in. In these cases, a local time can be specified. The recipient of an iCalendar object with a property value consisting of a local time, without any relative time zone information, SHOULD interpret the value as being fixed to whatever time zone the ATTENDEE is in at any given moment. This means that two ATTENDEEs may participate in the same event at different UTC times; floating time SHOULD only be used where that is reasonable behavior.
   In most cases, a fixed time is desired. To properly communicate a
   fixed time in a property value, either UTC time or local time with
   time zone reference MUST be specified.
   The use of local time in a TIME value without the TZID property
   parameter is to be interpreted as a local time value, regardless of
   the existence of "VTIMEZONE" calendar components in the iCalendar
   object.
   FORM #2: UTC TIME
   UTC time, or absolute time, is identified by a LATIN CAPITAL LETTER Z
   suffix character (US-ASCII decimal 90), the UTC designator, appended
   to the time value. For example, the following represents 07:00 AM
   UTC:
     070000Z

The TZID property parameter MUST NOT be applied to TIME properties whose time values are specified in UTC.
   FORM #3: LOCAL TIME AND TIME ZONE REFERENCE
   The local time with reference to time zone information form is
   identified by the use the TZID property parameter to reference the
   appropriate time zone definition. TZID is discussed in detail in the
   section on Time Zone.
   Example: The following represents 8:30 AM in New York in Winter, five
   hours behind UTC, in each of the three formats using the "X-
   TIMEOFDAY" non-standard property:
     X-TIMEOFDAY:083000

     X-TIMEOFDAY:133000Z

     X-TIMEOFDAY;TZID=US-Eastern:083000

4.3.13 URI

Value Name: URI

   Purpose: This value type is used to identify values that contain a
   uniform resource identifier (URI) type of reference to the property
   value.
   Formal Definition: The data type is defined by the following
   notation:
     uri        = <As defined by any IETF RFC>

Description: This data type might be used to reference binary information, for values that are large, or otherwise undesirable to include directly in the iCalendar object.
   The URI value formats in RFC 1738, RFC 2111 and any other IETF
   registered value format can be specified.
   Any IANA registered URI format can be used. These include, but are
   not limited to, those defined in RFC 1738 and RFC 2111.
   When a property parameter value is a URI value type, the URI MUST be
   specified as a quoted-string value.
   No additional content value encoding (i.e., BACKSLASH character
   encoding) is defined for this value type.
   Example: The following is a URI for a network file:
     http://host1.com/my-report.txt

4.3.14 UTC Offset

Value Name: UTC-OFFSET

   Purpose: This value type is used to identify properties that contain
   an offset from UTC to local time.
   Formal Definition: The data type is defined by the following
   notation:
     utc-offset = time-numzone  ;As defined above in time data type

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

Description: The PLUS SIGN character MUST be specified for positive UTC offsets (i.e., ahead of UTC). The value of "-0000" and "-000000" are not allowed. The time-second, if present, may not be 60; if absent, it defaults to zero.
   No additional content value encoding (i.e., BACKSLASH character
   encoding) is defined for this value type.
   Example: The following UTC offsets are given for standard time for
   New York (five hours behind UTC) and Geneva (one hour ahead of UTC):
     -0500

     +0100

4.4 iCalendar Object

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

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

The following is a simple example of an iCalendar object:
     BEGIN:VCALENDAR
     VERSION:2.0
     PRODID:-//hacksw/handcal//NONSGML v1.0//EN
     BEGIN:VEVENT
     DTSTART:19970714T170000Z
     DTEND:19970715T035959Z
     SUMMARY:Bastille Day Party
     END:VEVENT
     END:VCALENDAR

4.5 Property

A property is the definition of an individual attribute describing a calendar or a calendar component. A property takes the form defined by the "contentline" notation defined in section 4.1.1.

   The following is an example of a property:
     DTSTART:19960415T133000Z

This memo imposes no ordering of properties within an iCalendar object.
   Property names, parameter names and enumerated parameter values are
   case insensitive. For example, the property name "DUE" is the same as
   "due" and "Due", DTSTART;TZID=US-Eastern:19980714T120000 is the same
   as DtStart;TzID=US-Eastern:19980714T120000.

4.6 Calendar Components

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

   The body of the iCalendar object is defined by the following
   notation:
     icalbody   = calprops component

     calprops   = 2*(

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

                prodid /version /

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

                calscale        /
                method          /

                x-prop

                )

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

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

                  1*contentline

                  "END" ":" iana-token CRLF

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

                  1*contentline

                  "END" ":" x-name CRLF

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

4.6.1 Event Component

Component Name: "VEVENT"

   Purpose: Provide a grouping of component properties that describe an
   event.
   Format Definition: A "VEVENT" calendar component is defined by the
   following notation:
     eventc     = "BEGIN" ":" "VEVENT" CRLF
                  eventprop *alarmc
                  "END" ":" "VEVENT" CRLF

     eventprop  = *(

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

                class / created / description / dtstart / geo /

                last-mod / location / organizer / priority /
                dtstamp / seq / status / summary / transp /
                uid / url / recurid /

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

                dtend / duration /

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

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

                )

Description: A "VEVENT" calendar component is a grouping of component properties, and possibly including "VALARM" calendar components, that represents a scheduled amount of time on a calendar. For example, it can be an activity; such as a one-hour long, department meeting from 8:00 AM to 9:00 AM, tomorrow. Generally, an event will take up time on an individual calendar. Hence, the event will appear as an opaque interval in a search for busy time. Alternately, the event can have its Time Transparency set to "TRANSPARENT" in order to prevent blocking of the event in searches for busy time.
   The "VEVENT" is also the calendar component used to specify an
   anniversary or daily reminder within a calendar. These events have a
   DATE value type for the "DTSTART" property instead of the default
   data type of DATE-TIME. If such a "VEVENT" has a "DTEND" property, it
   MUST be specified as a DATE value also. The anniversary type of
   "VEVENT" can span more than one date (i.e, "DTEND" property value is
   set to a calendar date after the "DTSTART" property value).
   The "DTSTART" property for a "VEVENT" specifies the inclusive start
   of the event. For recurring events, it also specifies the very first
   instance in the recurrence set. The "DTEND" property for a "VEVENT"
   calendar component specifies the non-inclusive end of the event. For
   cases where a "VEVENT" calendar component specifies a "DTSTART"
   property with a DATE data type but no "DTEND" property, the events
   non-inclusive end is the end of the calendar date specified by the
   "DTSTART" property. For cases where a "VEVENT" calendar component
   specifies a "DTSTART" property with a DATE-TIME data type but no
   "DTEND" property, the event ends on the same calendar date and time
   of day specified by the "DTSTART" property.
   The "VEVENT" calendar component cannot be nested within another
   calendar component. However, "VEVENT" calendar components can be
   related to each other or to a "VTODO" or to a "VJOURNAL" calendar
   component with the "RELATED-TO" property.
   Example: The following is an example of the "VEVENT" calendar
   component used to represent a meeting that will also be opaque to
   searches for busy time:
     BEGIN:VEVENT
     UID:19970901T130000Z-123401@host.com
     DTSTAMP:19970901T1300Z
     DTSTART:19970903T163000Z
     DTEND:19970903T190000Z
     SUMMARY:Annual Employee Review
     CLASS:PRIVATE
     CATEGORIES:BUSINESS,HUMAN RESOURCES
     END:VEVENT

The following is an example of the "VEVENT" calendar component used to represent a reminder that will not be opaque, but rather transparent, to searches for busy time:
     BEGIN:VEVENT
     UID:19970901T130000Z-123402@host.com
     DTSTAMP:19970901T1300Z
     DTSTART:19970401T163000Z
     DTEND:19970402T010000Z
     SUMMARY:Laurel is in sensitivity awareness class.
     CLASS:PUBLIC
     CATEGORIES:BUSINESS,HUMAN RESOURCES
     TRANSP:TRANSPARENT
     END:VEVENT

The following is an example of the "VEVENT" calendar component used to represent an anniversary that will occur annually. Since it takes up no time, it will not appear as opaque in a search for busy time; no matter what the value of the "TRANSP" property indicates:
     BEGIN:VEVENT
     UID:19970901T130000Z-123403@host.com
     DTSTAMP:19970901T1300Z
     DTSTART:19971102
     SUMMARY:Our Blissful Anniversary
     CLASS:CONFIDENTIAL
     CATEGORIES:ANNIVERSARY,PERSONAL,SPECIAL OCCASION
     RRULE:FREQ=YEARLY
     END:VEVENT

4.6.2 To-do Component

Component Name: VTODO

   Purpose: Provide a grouping of calendar properties that describe a
   to-do.
   Formal Definition: A "VTODO" calendar component is defined by the
   following notation:
     todoc      = "BEGIN" ":" "VTODO" CRLF
                  todoprop *alarmc
                  "END" ":" "VTODO" CRLF

     todoprop   = *(

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

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

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

                due / duration /

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

                )

Description: A "VTODO" calendar component is a grouping of component properties and possibly "VALARM" calendar components that represent an action-item or assignment. For example, it can be used to represent an item of work assigned to an individual; such as "turn in travel expense today".
   The "VTODO" calendar component cannot be nested within another
   calendar component. However, "VTODO" calendar components can be
   related to each other or to a "VTODO" or to a "VJOURNAL" calendar
   component with the "RELATED-TO" property.
   A "VTODO" calendar component without the "DTSTART" and "DUE" (or
   "DURATION") properties specifies a to-do that will be associated with
   each successive calendar date, until it is completed.
   Example: The following is an example of a "VTODO" calendar component:
     BEGIN:VTODO
     UID:19970901T130000Z-123404@host.com
     DTSTAMP:19970901T1300Z
     DTSTART:19970415T133000Z
     DUE:19970416T045959Z
     SUMMARY:1996 Income Tax Preparation
     CLASS:CONFIDENTIAL
     CATEGORIES:FAMILY,FINANCE
     PRIORITY:1
     STATUS:NEEDS-ACTION
     END:VTODO

4.6.3 Journal Component

Component Name: VJOURNAL

   Purpose: Provide a grouping of component properties that describe a
   journal entry.
   Formal Definition: A "VJOURNAL" calendar component is defined by the
   following notation:
     journalc   = "BEGIN" ":" "VJOURNAL" CRLF
                  jourprop
                  "END" ":" "VJOURNAL" CRLF

     jourprop   = *(

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

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

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

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

                )

Description: A "VJOURNAL" calendar component is a grouping of component properties that represent one or more descriptive text notes associated with a particular calendar date. The "DTSTART" property is used to specify the calendar date that the journal entry is associated with. Generally, it will have a DATE value data type, but it can also be used to specify a DATE-TIME value data type. Examples of a journal entry include a daily record of a legislative body or a journal entry of individual telephone contacts for the day or an ordered list of accomplishments for the day. The "VJOURNAL" calendar component can also be used to associate a document with a calendar date.
   The "VJOURNAL" calendar component does not take up time on a
   calendar. Hence, it does not play a role in free or busy time
   searches - - it is as though it has a time transparency value of
   TRANSPARENT. It is transparent to any such searches.
   The "VJOURNAL" calendar component cannot be nested within another
   calendar component. However, "VJOURNAL" calendar components can be
   related to each other or to a "VEVENT" or to a "VTODO" calendar
   component, with the "RELATED-TO" property.
   Example: The following is an example of the "VJOURNAL" calendar
   component:
     BEGIN:VJOURNAL
     UID:19970901T130000Z-123405@host.com
     DTSTAMP:19970901T1300Z
     DTSTART;VALUE=DATE:19970317
     SUMMARY:Staff meeting minutes
     DESCRIPTION:1. Staff meeting: Participants include Joe\, Lisa
       and Bob. Aurora project plans were reviewed. There is currently
       no budget reserves for this project. Lisa will escalate to
       management. Next meeting on Tuesday.\n
       2. Telephone Conference: ABC Corp. sales representative called
       to discuss new printer. Promised to get us a demo by Friday.\n
       3. Henry Miller (Handsoff Insurance): Car was totaled by tree.
       Is looking into a loaner car. 654-2323 (tel).
     END:VJOURNAL

4.6.4 Free/Busy Component

Component Name: VFREEBUSY

   Purpose: Provide a grouping of component properties that describe
   either a request for free/busy time, describe a response to a request
   for free/busy time or describe a published set of busy time.
   Formal Definition: A "VFREEBUSY" calendar component is defined by the
   following notation:
     freebusyc  = "BEGIN" ":" "VFREEBUSY" CRLF
                  fbprop
                  "END" ":" "VFREEBUSY" CRLF

     fbprop     = *(

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

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

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

                attendee / comment / freebusy / rstatus / x-prop

                )

Description: A "VFREEBUSY" calendar component is a grouping of component properties that represents either a request for, a reply to a request for free or busy time information or a published set of busy time information.
   When used to request free/busy time information, the "ATTENDEE"
   property specifies the calendar users whose free/busy time is being
   requested; the "ORGANIZER" property specifies the calendar user who
   is requesting the free/busy time; the "DTSTART" and "DTEND"
   properties specify the window of time for which the free/busy time is
   being requested; the "UID" and "DTSTAMP" properties are specified to
   assist in proper sequencing of multiple free/busy time requests.
   When used to reply to a request for free/busy time, the "ATTENDEE"
   property specifies the calendar user responding to the free/busy time
   request; the "ORGANIZER" property specifies the calendar user that
   originally requested the free/busy time; the "FREEBUSY" property
   specifies the free/busy time information (if it exists); and the
   "UID" and "DTSTAMP" properties are specified to assist in proper
   sequencing of multiple free/busy time replies.
   When used to publish busy time, the "ORGANIZER" property specifies
   the calendar user associated with the published busy time; the
   "DTSTART" and "DTEND" properties specify an inclusive time window
   that surrounds the busy time information; the "FREEBUSY" property
   specifies the published busy time information; and the "DTSTAMP"
   property specifies the date/time that iCalendar object was created.
   The "VFREEBUSY" calendar component cannot be nested within another
   calendar component. Multiple "VFREEBUSY" calendar components can be
   specified within an iCalendar object. This permits the grouping of
   Free/Busy information into logical collections, such as monthly
   groups of busy time information.
   The "VFREEBUSY" calendar component is intended for use in iCalendar
   object methods involving requests for free time, requests for busy
   time, requests for both free and busy, and the associated replies.
   Free/Busy information is represented with the "FREEBUSY" property.
   This property provides a terse representation of time periods. One or
   more "FREEBUSY" properties can be specified in the "VFREEBUSY"
   calendar component.
   When present in a "VFREEBUSY" calendar component, the "DTSTART" and
   "DTEND" properties SHOULD be specified prior to any "FREEBUSY"
   properties. In a free time request, these properties can be used in
   combination with the "DURATION" property to represent a request for a
   duration of free time within a specified window of time.
   The recurrence properties ("RRULE", "EXRULE", "RDATE", "EXDATE") are
   not permitted within a "VFREEBUSY" calendar component. Any recurring
   events are resolved into their individual busy time periods using the
   "FREEBUSY" property.
   Example: The following is an example of a "VFREEBUSY" calendar
   component used to request free or busy time information:
     BEGIN:VFREEBUSY
     ORGANIZER:MAILTO:jane_doe@host1.com
     ATTENDEE:MAILTO:john_public@host2.com
     DTSTART:19971015T050000Z
     DTEND:19971016T050000Z
     DTSTAMP:19970901T083000Z
     END:VFREEBUSY

The following is an example of a "VFREEBUSY" calendar component used to reply to the request with busy time information:
     BEGIN:VFREEBUSY
     ORGANIZER:MAILTO:jane_doe@host1.com
     ATTENDEE:MAILTO:john_public@host2.com
     DTSTAMP:19970901T100000Z
     FREEBUSY;VALUE=PERIOD:19971015T050000Z/PT8H30M,
      19971015T160000Z/PT5H30M,19971015T223000Z/PT6H30M
     URL:http://host2.com/pub/busy/jpublic-01.ifb
     COMMENT:This iCalendar file contains busy time information for
       the next three months.
     END:VFREEBUSY

The following is an example of a "VFREEBUSY" calendar component used to publish busy time information.
     BEGIN:VFREEBUSY
     ORGANIZER:jsmith@host.com
     DTSTART:19980313T141711Z
     DTEND:19980410T141711Z
     FREEBUSY:19980314T233000Z/19980315T003000Z
     FREEBUSY:19980316T153000Z/19980316T163000Z
     FREEBUSY:19980318T030000Z/19980318T040000Z
     URL:http://www.host.com/calendar/busytime/jsmith.ifb
     END:VFREEBUSY

4.6.5 Time Zone Component

Component Name: VTIMEZONE

   Purpose: Provide a grouping of component properties that defines a
   time zone.
   Formal Definition: A "VTIMEZONE" calendar component is defined by the
   following notation:
     timezonec  = "BEGIN" ":" "VTIMEZONE" CRLF

                  2*(

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

                tzid /

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

                last-mod / tzurl /

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

                standardc / daylightc /

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

                  x-prop

                  )

                  "END" ":" "VTIMEZONE" CRLF

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

                  tzprop

                  "END" ":" "STANDARD" CRLF

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

                  tzprop

                  "END" ":" "DAYLIGHT" CRLF

     tzprop     = 3*(

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

                dtstart / tzoffsetto / tzoffsetfrom /

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

                comment / rdate / rrule / tzname / x-prop

                )

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

   daylight hours, often referred to as Daylight  Saving Time. Some
   locations adjust their time by a fraction of an hour. Standard Time
   is also known as Winter Time. Daylight Saving Time is also known as
   Advanced Time, Summer Time, or Legal Time in certain countries. The
   following table shows the changes in time zone rules in effect for
   New York City starting from 1967. Each line represents a description
   or rule for a particular observance.

     Effective Observance Rule

     Date       (Date/Time)             Offset  Abbreviation

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

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

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

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

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

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

        Note: The specification of a global time zone registry is not
        addressed by this document and is left for future study.
        However, implementers may find the Olson time zone database [TZ]
        a useful reference. It is an informal, public-domain collection
        of time zone information, which is currently being maintained by
        volunteer Internet participants, and is used in several
        operating systems. This database contains current and historical
        time zone information for a wide variety of locations around the
        globe; it provides a time zone identifier for every unique time
        zone rule set in actual use since 1970, with historical data
        going back to the introduction of standard time.

Interoperability between two calendaring and scheduling applications, especially for recurring events, to-dos or journal entries, is dependent on the ability to capture and convey date and time information in an unambiguous format. The specification of current time zone information is integral to this behavior.
   If present, the "VTIMEZONE" calendar component defines the set of
   Standard Time and Daylight Saving Time observances (or rules) for a
   particular time zone for a given interval of time. The "VTIMEZONE"
   calendar component cannot be nested within other calendar components.
   Multiple "VTIMEZONE" calendar components can exist in an iCalendar
   object. In this situation, each "VTIMEZONE" MUST represent a unique
   time zone definition. This is necessary for some classes of events,
   such as airline flights, that start in one time zone and end in
   another.
   The "VTIMEZONE" calendar component MUST be present if the iCalendar
   object contains an RRULE that generates dates on both sides of a time
   zone shift (e.g. both in Standard Time and Daylight Saving Time)
   unless the iCalendar object intends to convey a floating time (See
   the section "4.1.10.11 Time" for proper interpretation of floating
   time). It can be present if the iCalendar object does not contain
   such a RRULE. In addition, if a RRULE is present, there MUST be valid
   time zone information for all recurrence instances.
   The "VTIMEZONE" calendar component MUST include the "TZID" property
   and at least one definition of a standard or daylight component. The
   standard or daylight component MUST include the "DTSTART",
   "TZOFFSETFROM" and "TZOFFSETTO" properties.
   An individual "VTIMEZONE" calendar component MUST be specified for
   each unique "TZID" parameter value specified in the iCalendar object.
   Each "VTIMEZONE" calendar component consists of a collection of one
   or more sub-components that describe the rule for a particular
   observance (either a Standard Time or a Daylight Saving Time
   observance). The "STANDARD" sub-component consists of a collection of
   properties that describe Standard Time. The "DAYLIGHT" sub-component
   consists of a collection of properties that describe Daylight Saving
   Time. In general this collection of properties consists of:
        - the first onset date-time for the observance

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

        - the offset to be applied for the observance

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

        - an optional name for the observance

For a given time zone, there may be multiple unique definitions of the observances over a period of time. Each observance is described using either a "STANDARD" or "DAYLIGHT" sub-component. The collection of these sub-components is used to describe the time zone for a given period of time. The offset to apply at any given time is found by locating the observance that has the last onset date and time before the time in question, and using the offset value from that
   observance.
   The top-level properties in a "VTIMEZONE" calendar component are:
   The mandatory "TZID" property is a text value that uniquely
   identifies the VTIMZONE calendar component within the scope of an
   iCalendar object.
   The optional "LAST-MODIFIED" property is a UTC value that specifies
   the date and time that this time zone definition was last updated.
   The optional "TZURL" property is url value that points to a published
   VTIMEZONE definition. TZURL SHOULD refer to a resource that is
   accessible by anyone who might need to interpret the object. This
   SHOULD NOT normally be a file: URL or other URL that is not widely-
   accessible.
   The collection of properties that are used to define the STANDARD and
   DAYLIGHT sub-components include:
   The mandatory "DTSTART" property gives the effective onset date and
   local time for the time zone sub-component definition. "DTSTART" in
   this usage MUST be specified as a local DATE-TIME value.
   The mandatory "TZOFFSETFROM" property gives the UTC offset which is
   in use when the onset of this time zone observance begins.
   "TZOFFSETFROM" is combined with "DTSTART" to define the effective
   onset for the time zone sub-component definition. For example, the
   following represents the time at which the observance of Standard
   Time took effect in Fall 1967 for New York City:
     DTSTART:19671029T020000

     TZOFFSETFROM:-0400

The mandatory "TZOFFSETTO " property gives the UTC offset for the time zone sub-component (Standard Time or Daylight Saving Time) when this observance is in use.
   The optional "TZNAME" property is the customary name for the time
   zone. It may be specified multiple times, to allow for specifying
   multiple language variants of the time zone names. This could be used
   for displaying dates.
   If specified, the onset for the observance defined by the time zone
   sub-component is defined by either the "RRULE" or "RDATE" property.
   If neither is specified, only one sub-component can be specified in
   the "VTIMEZONE" calendar component and it is assumed that the single
   observance specified is always in effect.
   The "RRULE" property defines the recurrence rule for the onset of the
   observance defined by this time zone sub-component. Some specific
   requirements for the usage of RRULE for this purpose include:
        - If observance is known to have an effective end date, the
        "UNTIL" recurrence rule parameter MUST be used to specify the
        last valid onset of this observance (i.e., the UNTIL date-time
        will be equal to the last instance generated by the recurrence
        pattern). It MUST be specified in UTC time.

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

Alternatively, the "RDATE" property can be used to define the onset of the observance by giving the individual onset date and times. "RDATE" in this usage MUST be specified as a local DATE-TIME value in UTC time.
   The optional "COMMENT" property is also allowed for descriptive
   explanatory text.
   Example: The following are examples of the "VTIMEZONE" calendar
   component:
   This is an example showing time zone information for the Eastern
   United States using "RDATE" property. Note that this is only suitable
   for a recurring event that starts on or later than April 6, 1997 at
   03:00:00 EDT (i.e., the earliest effective transition date and time)
   and ends no later than April 7, 1998 02:00:00 EST (i.e., latest valid
   date and time for EST in this scenario). For example, this can be
   used for a recurring event that occurs every Friday, 8am-9:00 AM,
   starting June 1, 1997, ending December 31, 1997.
     BEGIN:VTIMEZONE
     TZID:US-Eastern
     LAST-MODIFIED:19870101T000000Z
     BEGIN:STANDARD
     DTSTART:19971026T020000
     RDATE:19971026T020000
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     BEGIN:DAYLIGHT
     DTSTART:19971026T020000

     RDATE:19970406T020000
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     END:VTIMEZONE

This is a simple example showing the current time zone rules for the Eastern United States using a RRULE recurrence pattern. Note that there is no effective end date to either of the Standard Time or Daylight Time rules. This information would be valid for a recurring event starting today and continuing indefinitely.
     BEGIN:VTIMEZONE
     TZID:US-Eastern
     LAST-MODIFIED:19870101T000000Z
     TZURL:http://zones.stds_r_us.net/tz/US-Eastern
     BEGIN:STANDARD
     DTSTART:19671029T020000
     RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     BEGIN:DAYLIGHT
     DTSTART:19870405T020000
     RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     END:VTIMEZONE

This is an example showing a fictitious set of rules for the Eastern United States, where the Daylight Time rule has an effective end date (i.e., after that date, Daylight Time is no longer observed).
     BEGIN:VTIMEZONE
     TZID:US--Fictitious-Eastern
     LAST-MODIFIED:19870101T000000Z
     BEGIN:STANDARD
     DTSTART:19671029T020000
     RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD

     BEGIN:DAYLIGHT
     DTSTART:19870405T020000
     RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4;UNTIL=19980404T070000Z
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     END:VTIMEZONE

This is an example showing a fictitious set of rules for the Eastern United States, where the first Daylight Time rule has an effective end date. There is a second Daylight Time rule that picks up where the other left off.
     BEGIN:VTIMEZONE
     TZID:US--Fictitious-Eastern
     LAST-MODIFIED:19870101T000000Z
     BEGIN:STANDARD
     DTSTART:19671029T020000
     RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     BEGIN:DAYLIGHT
     DTSTART:19870405T020000
     RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4;UNTIL=19980404T070000Z
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     BEGIN:DAYLIGHT
     DTSTART:19990424T020000
     RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=4
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     END:VTIMEZONE

4.6.6 Alarm Component

Component Name: VALARM

   Purpose: Provide a grouping of component properties that define an
   alarm.
   Formal Definition: A "VALARM" calendar component is defined by the
   following notation:
          alarmc     = "BEGIN" ":" "VALARM" CRLF
                       (audioprop / dispprop / emailprop / procprop)
                       "END" ":" "VALARM" CRLF

     audioprop  = 2*(

                ; 'action' and 'trigger' are both REQUIRED,
                ; but MUST NOT occur more than once

                action / trigger /

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

                duration / repeat /

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

                attach /

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

                x-prop

                )

     dispprop   = 3*(

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

                action / description / trigger /

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

                duration / repeat /

                ; the following is optional,

                ; and MAY occur more than once

                *x-prop

                )

     emailprop  = 5*(

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

                action / description / trigger / summary

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

                attendee /

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

                duration / repeat /

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

                attach / x-prop

                )

     procprop   = 3*(

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

                action / attach / trigger /

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

                duration / repeat /

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

                description /

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

                x-prop

                )

Description: A "VALARM" calendar component is a grouping of component properties that is a reminder or alarm for an event or a to-do. For example, it may be used to define a reminder for a pending event or an overdue to-do.
   The "VALARM" calendar component MUST include the "ACTION" and
   "TRIGGER" properties. The "ACTION" property further constrains the
   "VALARM" calendar component in the following ways:
   When the action is "AUDIO", the alarm can also include one and only
   one "ATTACH" property, which MUST point to a sound resource, which is
   rendered when the alarm is triggered.
   When the action is "DISPLAY", the alarm MUST also include a
   "DESCRIPTION" property, which contains the text to be displayed when
   the alarm is triggered.
   When the action is "EMAIL", the alarm MUST include a "DESCRIPTION"
   property, which contains the text to be used as the message body, a
   "SUMMARY" property, which contains the text to be used as the message
   subject, and one or more "ATTENDEE" properties, which contain the
   email address of attendees to receive the message. It can also
   include one or more "ATTACH" properties, which are intended to be
   sent as message attachments. When the alarm is triggered, the email
   message is sent.
   When the action is "PROCEDURE", the alarm MUST include one and only
   one "ATTACH" property, which MUST point to a procedure resource,
   which is invoked when the alarm is triggered.
   The "VALARM" calendar component MUST only appear within either a
   "VEVENT" or "VTODO" calendar component. "VALARM" calendar components
   cannot be nested. Multiple mutually independent "VALARM" calendar
   components can be specified for a single "VEVENT" or "VTODO" calendar
   component.
   The "TRIGGER" property specifies when the alarm will be triggered.
   The "TRIGGER" property specifies a duration prior to the start of an
   event or a to-do. The "TRIGGER" edge may be explicitly set to be
   relative to the "START" or "END" of the event or to-do with the
   "RELATED" parameter of the "TRIGGER" property. The "TRIGGER" property
   value type can alternatively be set to an absolute calendar date and
   time of day value.
   In an alarm set to trigger on the "START" of an event or to-do, the
   "DTSTART" property MUST be present in the associated event or to-do.
   In an alarm in a "VEVENT" calendar component set to trigger on the
   "END" of the event, either the "DTEND" property MUST be present, or
   the "DTSTART" and "DURATION" properties MUST both be present. In an
   alarm in a "VTODO" calendar component set to trigger on the "END" of
   the to-do, either the "DUE" property MUST be present, or the
   "DTSTART" and "DURATION" properties MUST both be present.
   The alarm can be defined such that it triggers repeatedly. A
   definition of an alarm with a repeating trigger MUST include both the
   "DURATION" and "REPEAT" properties. The "DURATION" property specifies
   the delay period, after which the alarm will repeat. The "REPEAT"
   property specifies the number of additional repetitions that the
   alarm will triggered. This repitition count is in addition to the
   initial triggering of the alarm. Both of these properties MUST be
   present in order to specify a repeating alarm. If one of these two
   properties is absent, then the alarm will not repeat beyond the
   initial trigger.
   The "ACTION" property is used within the "VALARM" calendar component
   to specify the type of action invoked when the alarm is triggered.
   The "VALARM" properties provide enough information for a specific
   action to be invoked. It is typically the responsibility of a
   "Calendar User Agent" (CUA) to deliver the alarm in the specified
   fashion. An "ACTION" property value of AUDIO specifies an alarm that
   causes a sound to be played to alert the user; DISPLAY specifies an
   alarm that causes a text message to be displayed to the user; EMAIL
   specifies an alarm that causes an electronic email message to be
   delivered to one or more email addresses; and PROCEDURE specifies an
   alarm that causes a procedure to be executed. The "ACTION" property
   MUST specify one and only one of these values.
   In an AUDIO alarm, if the optional "ATTACH" property is included, it
   MUST specify an audio sound resource. The intention is that the sound
   will be played as the alarm effect. If an "ATTACH" property is
   specified that does not refer to a sound resource, or if the
   specified sound resource cannot be rendered (because its format is
   unsupported, or because it cannot be retrieved), then the CUA or
   other entity responsible for playing the sound may choose a fallback
   action, such as playing a built-in default sound, or playing no sound
   at all.
   In a DISPLAY alarm, the intended alarm effect is for the text value
   of the "DESCRIPTION" property to be displayed to the user.
   In an EMAIL alarm, the intended alarm effect is for an email message
   to be composed and delivered to all the addresses specified by the
   "ATTENDEE" properties in the "VALARM" calendar component. The
   "DESCRIPTION" property of the "VALARM" calendar component MUST be
   used as the body text of the message, and the "SUMMARY" property MUST
   be used as the subject text. Any "ATTACH" properties in the "VALARM"
   calendar component SHOULD be sent as attachments to the message.
   In a PROCEDURE alarm, the "ATTACH" property in the "VALARM" calendar
   component MUST specify a procedure or program that is intended to be
   invoked as the alarm effect. If the procedure or program is in a
   format that cannot be rendered, then no procedure alarm will be
   invoked. If the "DESCRIPTION" property is present, its value
   specifies the argument string to be passed to the procedure or
   program. "Calendar User Agents" that receive an iCalendar object with
   this category of alarm, can disable or allow the "Calendar User" to
   disable, or otherwise ignore this type of alarm. While a very useful
   alarm capability, the PROCEDURE type of alarm SHOULD be treated by
   the "Calendar User Agent" as a potential security risk.
   Example: The following example is for a "VALARM" calendar component
   that specifies an audio alarm that will sound at a precise time and
   repeat 4 more times at 15 minute intervals:
     BEGIN:VALARM
     TRIGGER;VALUE=DATE-TIME:19970317T133000Z
     REPEAT:4
     DURATION:PT15M
     ACTION:AUDIO
     ATTACH;FMTTYPE=audio/basic:ftp://host.com/pub/sounds/bell-01.aud
     END:VALARM

The following example is for a "VALARM" calendar component that specifies a display alarm that will trigger 30 minutes before the scheduled start of the event or the due date/time of the to-do it is associated with and will repeat 2 more times at 15 minute intervals:
     BEGIN:VALARM
     TRIGGER:-PT30M
     REPEAT:2
     DURATION:PT15M
     ACTION:DISPLAY

     DESCRIPTION:Breakfast meeting with executive\n
      team at 8:30 AM EST.
     END:VALARM

The following example is for a "VALARM" calendar component that specifies an email alarm that will trigger 2 days before the scheduled due date/time of a to-do it is associated with. It does not repeat. The email has a subject, body and attachment link.
     BEGIN:VALARM
     TRIGGER:-P2D
     ACTION:EMAIL
     ATTENDEE:MAILTO:john_doe@host.com
     SUMMARY:*** REMINDER: SEND AGENDA FOR WEEKLY STAFF MEETING ***
     DESCRIPTION:A draft agenda needs to be sent out to the attendees
       to the weekly managers meeting (MGR-LIST). Attached is a
       pointer the document template for the agenda file.
     ATTACH;FMTTYPE=application/binary:http://host.com/templates/agen
      da.doc
     END:VALARM

The following example is for a "VALARM" calendar component that specifies a procedural alarm that will trigger at a precise date/time and will repeat 23 more times at one hour intervals. The alarm will invoke a procedure file.
     BEGIN:VALARM
     TRIGGER;VALUE=DATE-TIME:19980101T050000Z
     REPEAT:23
     DURATION:PT1H
     ACTION:PROCEDURE
     ATTACH;FMTTYPE=application/binary:ftp://host.com/novo-
      procs/felizano.exe
     END:VALARM

4.7 Calendar Properties

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


4.7.1 Calendar Scale

Property Name: CALSCALE

   Purpose: This property defines the calendar scale used for the
   calendar information specified in the iCalendar object.
   Value Type: TEXT
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: Property can be specified in an iCalendar object. The
   default value is "GREGORIAN".
   Description: This memo is based on the Gregorian calendar scale. The
   Gregorian calendar scale is assumed if this property is not specified
   in the iCalendar object. It is expected that other calendar scales
   will be defined in other specifications or by future versions of this
   memo.
   Format Definition: The property is defined by the following notation:
     calscale   = "CALSCALE" calparam ":" calvalue CRLF

     calparam   = *(";" xparam)

     calvalue   = "GREGORIAN" / iana-token

Example: The following is an example of this property:
     CALSCALE:GREGORIAN

4.7.2 Method

Property Name: METHOD

   Purpose: This property defines the iCalendar object method associated
   with the calendar object.
   Value Type: TEXT
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: The property can be specified in an iCalendar object.
   Description: When used in a MIME message entity, the value of this
   property MUST be the same as the Content-Type "method" parameter
   value. This property can only appear once within the iCalendar
   object. If either the "METHOD" property or the Content-Type "method"
   parameter is specified, then the other MUST also be specified.
   No methods are defined by this specification. This is the subject of
   other specifications, such as the iCalendar Transport-independent
   Interoperability Protocol (iTIP) defined by [ITIP].
   If this property is not present in the iCalendar object, then a
   scheduling transaction MUST NOT be assumed. In such cases, the
   iCalendar object is merely being used to transport a snapshot of some
   calendar information; without the intention of conveying a scheduling
   semantic.
   Format Definition: The property is defined by the following notation:
     method     = "METHOD" metparam ":" metvalue CRLF

     metparam   = *(";" xparam)

     metvalue   = iana-token

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

4.7.3 Product Identifier

Property Name: PRODID

   Purpose: This property specifies the identifier for the product that
   created the iCalendar object.
   Value Type: TEXT
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: The property MUST be specified once in an iCalendar
   object.
   Description: The vendor of the implementation SHOULD assure that this
   is a globally unique identifier; using some technique such as an FPI
   value, as defined in [ISO 9070].
   This property SHOULD not be used to alter the interpretation of an
   iCalendar object beyond the semantics specified in this memo. For
   example, it is not to be used to further the understanding of non-
   standard properties.
   Format Definition: The property is defined by the following notation:
     prodid     = "PRODID" pidparam ":" pidvalue CRLF

     pidparam   = *(";" xparam)

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

Example: The following is an example of this property. It does not imply that English is the default language.
     PRODID:-//ABC Corporation//NONSGML My Product//EN

4.7.4 Version

Property Name: VERSION

   Purpose: This property specifies the identifier corresponding to the
   highest version number or the minimum and maximum range of the
   iCalendar specification that is required in order to interpret the
   iCalendar object.
   Value Type: TEXT
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property MUST be specified by an iCalendar object,
   but MUST only be specified once.
   Description: A value of "2.0" corresponds to this memo.
   Format Definition: The property is defined by the following notation:
     version    = "VERSION" verparam ":" vervalue CRLF

     verparam   = *(";" xparam)

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

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

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

Example: The following is an example of this property:
     VERSION:2.0

4.8 Component Properties

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


4.8.1 Descriptive Component Properties

The following properties specify descriptive information about calendar components.


4.8.1.1 Attachment

Property Name: ATTACH

   Purpose: The property provides the capability to associate a document
   object with a calendar component.
   Value Type: The default value type for this property is URI. The
   value type can also be set to BINARY to indicate inline binary
   encoded content information.
   Property Parameters: Non-standard, inline encoding, format type and
   value data type property parameters can be specified on this
   property.
   Conformance: The property can be specified in a "VEVENT", "VTODO",
   "VJOURNAL" or "VALARM" calendar components.
   Description: The property can be specified within "VEVENT", "VTODO",
   "VJOURNAL", or "VALARM" calendar components. This property can be
   specified multiple times within an iCalendar object.
   Format Definition: The property is defined by the following notation:
     attach     = "ATTACH" attparam ":" uri  CRLF

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

     attparam   = *(

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

                (";" fmttypeparam) /

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

                (";" xparam)

                )

Example: The following are examples of this property:
     ATTACH:CID:jsmith.part3.960817T083000.xyzMail@host1.com

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

4.8.1.2 Categories

Property Name: CATEGORIES

   Purpose: This property defines the categories for a calendar
   component.
   Value Type: TEXT
   Property Parameters: Non-standard and language property parameters
   can be specified on this property.
   Conformance: The property can be specified within "VEVENT", "VTODO"
   or "VJOURNAL" calendar components.
   Description: This property is used to specify categories or subtypes
   of the calendar component. The categories are useful in searching for
   a calendar component of a particular type and category. Within the
   "VEVENT", "VTODO" or "VJOURNAL" calendar components, more than one
   category can be specified as a list of categories separated by the
   COMMA character (US-ASCII decimal 44).
   Format Definition: The property is defined by the following notation:
     categories = "CATEGORIES" catparam ":" text *("," text)
                  CRLF

     catparam   = *(

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

                (";" languageparam ) /

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

                (";" xparam)

                )

Example: The following are examples of this property:
     CATEGORIES:APPOINTMENT,EDUCATION

     CATEGORIES:MEETING

4.8.1.3 Classification

Property Name: CLASS

   Purpose: This property defines the access classification for a
   calendar component.
   Value Type: TEXT
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: The property can be specified once in a "VEVENT",
   "VTODO" or "VJOURNAL" calendar components.
   Description: An access classification is only one component of the
   general security system within a calendar application. It provides a
   method of capturing the scope of the access the calendar owner
   intends for information within an individual calendar entry. The
   access classification of an individual iCalendar component is useful
   when measured along with the other security components of a calendar
   system (e.g., calendar user authentication, authorization, access
   rights, access role, etc.). Hence, the semantics of the individual
   access classifications cannot be completely defined by this memo
   alone. Additionally, due to the "blind" nature of most exchange
   processes using this memo, these access classifications cannot serve
   as an enforcement statement for a system receiving an iCalendar
   object. Rather, they provide a method for capturing the intention of
   the calendar owner for the access to the calendar component.
   Format Definition: The property is defined by the following notation:
     class      = "CLASS" classparam ":" classvalue CRLF

     classparam = *(";" xparam)

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

Example: The following is an example of this property:
     CLASS:PUBLIC

4.8.1.4 Comment

Property Name: COMMENT

   Purpose: This property specifies non-processing information intended
   to provide a comment to the calendar user.
   Value Type: TEXT
   Property Parameters: Non-standard, alternate text representation and
   language property parameters can be specified on this property.
   Conformance: This property can be specified in "VEVENT", "VTODO",
   "VJOURNAL", "VTIMEZONE" or "VFREEBUSY" calendar components.
   Description: The property can be specified multiple times.
   Format Definition: The property is defined by the following notation:
     comment    = "COMMENT" commparam ":" text CRLF

     commparam  = *(

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

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

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

                (";" xparam)

                )

Example: The following is an example of this property:
     COMMENT:The meeting really needs to include both ourselves
       and the customer. We can't hold this  meeting without them.
       As a matter of fact\, the venue for the meeting ought to be at

       their site. - - John

The data type for this property is TEXT.

4.8.1.5 Description

Property Name: DESCRIPTION

   Purpose: This property provides a more complete description of the
   calendar component, than that provided by the "SUMMARY" property.
   Value Type: TEXT
   Property Parameters: Non-standard, alternate text representation and
   language property parameters can be specified on this property.
   Conformance: The property can be specified in the "VEVENT", "VTODO",
   "VJOURNAL" or "VALARM" calendar components. The property can be
   specified multiple times only within a "VJOURNAL" calendar component.
   Description: This property is used in the "VEVENT" and "VTODO" to
   capture lengthy textual decriptions associated with the activity.
   This property is used in the "VJOURNAL" calendar component to capture
   one more textual journal entries.
   This property is used in the "VALARM" calendar component to capture
   the display text for a DISPLAY category of alarm, to capture the body
   text for an EMAIL category of alarm and to capture the argument
   string for a PROCEDURE category of alarm.
   Format Definition: The property is defined by the following notation:
     description        = "DESCRIPTION" descparam ":" text CRLF

     descparam  = *(

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

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

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

                (";" xparam)

                )

Example: The following is an example of the property with formatted line breaks in the property value:
     DESCRIPTION:Meeting to provide technical review for "Phoenix"
       design.\n Happy Face Conference Room. Phoenix design team
       MUST attend this meeting.\n RSVP to team leader.

The following is an example of the property with folding of long lines:
     DESCRIPTION:Last draft of the new novel is to be completed
       for the editor's proof today.

4.8.1.6 Geographic Position

Property Name: GEO

   Purpose: This property specifies information related to the global
   position for the activity specified by a calendar component.
   Value Type: FLOAT. The value MUST be two SEMICOLON separated FLOAT
   values.
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property can be specified in  "VEVENT" or "VTODO"
   calendar components.

Description: The property value specifies latitude and longitude, in that order (i.e., "LAT LON" ordering). The longitude represents the location east or west of the prime meridian as a positive or negative real number, respectively. The longitude and latitude values MAY be specified up to six decimal places, which will allow for accuracy to within one meter of geographical position. Receiving applications MUST accept values of this precision and MAY truncate values of greater precision.
   Values for latitude and longitude shall be expressed as decimal
   fractions of degrees. Whole degrees of latitude shall be represented
   by a two-digit decimal number ranging from 0 through 90. Whole
   degrees of longitude shall be represented by a decimal number ranging
   from 0 through 180. When a decimal fraction of a degree is specified,
   it shall be separated from the whole number of degrees by a decimal
   point.
   Latitudes north of the equator shall be specified by a plus sign (+),
   or by the absence of a minus sign (-), preceding the digits
   designating degrees. Latitudes south of the Equator shall be
   designated by a minus sign (-) preceding the digits designating
   degrees. A point on the Equator shall be assigned to the Northern
   Hemisphere.
   Longitudes east of the prime meridian shall be specified by a plus
   sign (+), or by the absence of a minus sign (-), preceding the digits
   designating degrees. Longitudes west of the meridian shall be
   designated by minus sign (-) preceding the digits designating
   degrees. A point on the prime meridian shall be assigned to the
   Eastern Hemisphere. A point on the 180th meridian shall be assigned
   to the Western Hemisphere. One exception to this last convention is
   permitted. For the special condition of describing a band of latitude
   around the earth, the East Bounding Coordinate data element shall be
   assigned the value +180 (180) degrees.
   Any spatial address with a latitude of +90 (90) or -90 degrees will
   specify the position at the North or South Pole, respectively. The
   component for longitude may have any legal value.
   With the exception of the special condition described above, this
   form is specified in Department of Commerce, 1986, Representation of
   geographic point locations for information interchange (Federal
   Information Processing Standard 70-1):  Washington,  Department of
   Commerce, National Institute of Standards and Technology.

The simple formula for converting degrees-minutes-seconds into decimal degrees is:
     decimal = degrees + minutes/60 + seconds/3600.

Format Definition: The property is defined by the following notation:
     geo        = "GEO" geoparam ":" geovalue CRLF

     geoparam   = *(";" xparam)

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

Example: The following is an example of this property:
     GEO:37.386013;-122.082932

4.8.1.7 Location

Property Name: LOCATION

   Purpose: The property defines the intended venue for the activity
   defined by a calendar component.
   Value Type: TEXT
   Property Parameters: Non-standard, alternate text representation and
   language property parameters can be specified on this property.
   Conformance: This property can be specified in "VEVENT" or "VTODO"
   calendar component.
   Description: Specific venues such as conference or meeting rooms may
   be explicitly specified using this property. An alternate
   representation may be specified that is a URI that points to
   directory information with more structured specification of the
   location. For example, the alternate representation may specify
   either an LDAP URI pointing to an LDAP server entry or a CID URI
   pointing to a MIME body part containing a vCard [RFC 2426] for the
   location.
   Format Definition: The property is defined by the following notation:
     location   = "LOCATION locparam ":" text CRLF

     locparam   = *(

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

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

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

                (";" xparam)

                )

Example: The following are some examples of this property:
     LOCATION:Conference Room - F123, Bldg. 002

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

4.8.1.8 Percent Complete

Property Name: PERCENT-COMPLETE

   Purpose: This property is used by an assignee or delegatee of a to-do
   to convey the percent completion of a to-do to the Organizer.
   Value Type: INTEGER
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property can be specified in a "VTODO" calendar
   component.
   Description: The property value is a positive integer between zero
   and one hundred. A value of "0" indicates the to-do has not yet been
   started. A value of "100" indicates that the to-do has been
   completed. Integer values in between indicate the percent partially
   complete.
   When a to-do is assigned to multiple individuals, the property value
   indicates the percent complete for that portion of the to-do assigned
   to the assignee or delegatee. For example, if a to-do is assigned to
   both individuals "A" and "B". A reply from "A" with a percent
   complete of "70" indicates that "A" has completed 70% of the to-do
   assigned to them. A reply from "B" with a percent complete of "50"
   indicates "B" has completed 50% of the to-do assigned to them.
   Format Definition: The property is defined by the following notation:
     percent = "PERCENT-COMPLETE" pctparam ":" integer CRLF

     pctparam   = *(";" xparam)

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

4.8.1.9 Priority

Property Name: PRIORITY

   Purpose: The property defines the relative priority for a calendar
   component.
   Value Type: INTEGER
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: The property can be specified in a "VEVENT" or "VTODO"
   calendar component.
   Description: The priority is specified as an integer in the range
   zero to nine. A value of zero (US-ASCII decimal 48) specifies an
   undefined priority. A value of one (US-ASCII decimal 49) is the
   highest priority. A value of two (US-ASCII decimal 50) is the second
   highest priority. Subsequent numbers specify a decreasing ordinal
   priority. A value of nine (US-ASCII decimal 58) is the lowest
   priority.
   A CUA with a three-level priority scheme of "HIGH", "MEDIUM" and
   "LOW" is mapped into this property such that a property value in the
   range of one (US-ASCII decimal 49) to four (US-ASCII decimal 52)
   specifies "HIGH" priority. A value of five (US-ASCII decimal 53) is
   the normal or "MEDIUM" priority. A value in the range of six (US-
   ASCII decimal 54) to nine (US-ASCII decimal 58) is "LOW" priority.
   A CUA with a priority schema of "A1", "A2", "A3", "B1", "B2", ...,
   "C3" is mapped into this property such that a property value of one
   (US-ASCII decimal 49) specifies "A1", a property value of two (US-
   ASCII decimal 50) specifies "A2", a property value of three (US-ASCII
   decimal 51) specifies "A3", and so forth up to a property value of 9
   (US-ASCII decimal 58) specifies "C3".
   Other integer values are reserved for future use.
   Within a "VEVENT" calendar component, this property specifies a
   priority for the event. This property may be useful when more than
   one event is scheduled for a given time period.
   Within a "VTODO" calendar component, this property specified a
   priority for the to-do. This property is useful in prioritizing
   multiple action items for a given time period.
   Format Definition: The property is specified by the following
   notation:
     priority   = "PRIORITY" prioparam ":" privalue CRLF
     ;Default is zero

     prioparam  = *(";" xparam)

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

The following is an example of a property with the highest priority:
     PRIORITY:1

The following is an example of a property with a next highest priority:
     PRIORITY:2

Example: The following is an example of a property with no priority. This is equivalent to not specifying the "PRIORITY" property:
     PRIORITY:0

4.8.1.10 Resources

Property Name: RESOURCES

   Purpose: This property defines the equipment or resources anticipated
   for an activity specified by a calendar entity..
   Value Type: TEXT
   Property Parameters: Non-standard, alternate text representation and
   language property parameters can be specified on this property.
   Conformance: This property can be specified in "VEVENT" or "VTODO"
   calendar component.
   Description: The property value is an arbitrary text. More than one
   resource can be specified as a list of resources separated by the
   COMMA character (US-ASCII decimal 44).
   Format Definition: The property is defined by the following notation:
     resources  = "RESOURCES" resrcparam ":" text *("," text) CRLF

     resrcparam = *(

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

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

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

                (";" xparam)

                )

Example: The following is an example of this property:
     RESOURCES:EASEL,PROJECTOR,VCR

     RESOURCES;LANGUAGE=fr:1 raton-laveur

4.8.1.11 Status

Property Name: STATUS

   Purpose: This property defines the overall status or confirmation for
   the calendar component.
   Value Type: TEXT
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property can be specified in "VEVENT", "VTODO" or
   "VJOURNAL" calendar components.
   Description: In a group scheduled calendar component, the property is
   used by the "Organizer" to provide a confirmation of the event to the
   "Attendees". For example in a "VEVENT" calendar component, the
   "Organizer" can indicate that a meeting is tentative, confirmed or
   cancelled. In a "VTODO" calendar component, the "Organizer" can
   indicate that an action item needs action, is completed, is in
   process or being worked on, or has been cancelled. In a "VJOURNAL"
   calendar component, the "Organizer" can indicate that a journal entry
   is draft, final or has been cancelled or removed.
   Format Definition: The property is defined by the following notation:
     status     = "STATUS" statparam] ":" statvalue CRLF

     statparam  = *(";" xparam)

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

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

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

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

The following is an example of this property for a "VTODO" calendar component:
     STATUS:NEEDS-ACTION

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

4.8.1.12 Summary

Property Name: SUMMARY

   Purpose: This property defines a short summary or subject for the
   calendar component.
   Value Type: TEXT
   Property Parameters: Non-standard, alternate text representation and
   language property parameters can be specified on this property.
   Conformance: The property can be specified in "VEVENT", "VTODO",
   "VJOURNAL" or "VALARM" calendar components.
   Description: This property is used in the "VEVENT", "VTODO" and
   "VJOURNAL" calendar components to capture a short, one line summary
   about the activity or journal entry.
   This property is used in the "VALARM" calendar component to capture
   the subject of an EMAIL category of alarm.
   Format Definition: The property is defined by the following notation:
     summary    = "SUMMARY" summparam ":" text CRLF

     summparam  = *(

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

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

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

                (";" xparam)

                )

Example: The following is an example of this property:
     SUMMARY:Department Party

4.8.2 Date and Time Component Properties

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


4.8.2.1 Date/Time Completed

Property Name: COMPLETED

   Purpose: This property defines the date and time that a to-do was
   actually completed.
   Value Type: DATE-TIME
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: The property can be specified in a "VTODO" calendar
   component.
   Description: The date and time MUST be in a UTC format.
   Format Definition: The property is defined by the following notation:
     completed  = "COMPLETED" compparam ":" date-time CRLF

     compparam  = *(";" xparam)

Example: The following is an example of this property:
     COMPLETED:19960401T235959Z

4.8.2.2 Date/Time End

Property Name: DTEND

   Purpose: This property specifies the date and time that a calendar
   component ends.
   Value Type: The default value type is DATE-TIME. The value type can
   be set to a DATE value type.
   Property Parameters: Non-standard, value data type, time zone
   identifier property parameters can be specified on this property.
   Conformance: This property can be specified in "VEVENT" or
   "VFREEBUSY" calendar components.
   Description: Within the "VEVENT" calendar component, this property
   defines the date and time by which the event ends. The value MUST be
   later in time than the value of the "DTSTART" property.
   Within the "VFREEBUSY" calendar component, this property defines the
   end date and time for the free or busy time information. The time
   MUST be specified in the UTC time format. The value MUST be later in
   time than the value of the "DTSTART" property.
   Format Definition: The property is defined by the following notation:
     dtend      = "DTEND" dtendparam":" dtendval CRLF

     dtendparam = *(

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

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

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

                (";" xparam)

                )

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

Example: The following is an example of this property:
     DTEND:19960401T235959Z

     DTEND;VALUE=DATE:19980704

4.8.2.3 Date/Time Due

Property Name: DUE

   Purpose: This property defines the date and time that a to-do is
   expected to be completed.
   Value Type: The default value type is DATE-TIME. The value type can
   be set to a DATE value type.
   Property Parameters: Non-standard, value data type, time zone
   identifier property parameters can be specified on this property.
   Conformance: The property can be specified once in a "VTODO" calendar
   component.
   Description: The value MUST be a date/time equal to or after the
   DTSTART value, if specified.
   Format Definition: The property is defined by the following notation:
     due        = "DUE" dueparam":" dueval CRLF

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

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

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

                  *(";" xparam)

                )

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

Example: The following is an example of this property:
     DUE:19980430T235959Z

4.8.2.4 Date/Time Start

Property Name: DTSTART

   Purpose: This property specifies when the calendar component begins.
   Value Type: The default value type is DATE-TIME. The time value MUST
   be one of the forms defined for the DATE-TIME value type. The value
   type can be set to a DATE value type.
   Property Parameters: Non-standard, value data type, time zone
   identifier property parameters can be specified on this property.
   Conformance: This property can be specified in the "VEVENT", "VTODO",
   "VFREEBUSY", or "VTIMEZONE" calendar components.
   Description: Within the "VEVENT" calendar component, this property
   defines the start date and time for the event. The property is
   REQUIRED in "VEVENT" calendar components. Events can have a start
   date/time but no end date/time. In that case, the event does not take
   up any time.
   Within the "VFREEBUSY" calendar component, this property defines the
   start date and time for the free or busy time information. The time
   MUST be specified in UTC time.
   Within the "VTIMEZONE" calendar component, this property defines the
   effective start date and time for a time zone specification. This
   property is REQUIRED within each STANDARD and DAYLIGHT part included
   in "VTIMEZONE" calendar components and MUST be specified as a local
   DATE-TIME without the "TZID" property parameter.
   Format Definition: The property is defined by the following notation:
     dtstart    = "DTSTART" dtstparam ":" dtstval CRLF

     dtstparam  = *(

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

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

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

                  *(";" xparam)

                )

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

Example: The following is an example of this property:
     DTSTART:19980118T073000Z

4.8.2.5 Duration

Property Name: DURATION

   Purpose: The property specifies a positive duration of time.
   Value Type: DURATION
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: The property can be specified in "VEVENT", "VTODO",
   "VFREEBUSY" or "VALARM" calendar components.
   Description: In a "VEVENT" calendar component the property may be
   used to specify a duration of the event, instead of an explicit end
   date/time. In a "VTODO" calendar component the property may be used
   to specify a duration for the to-do, instead of an explicit due
   date/time. In a "VFREEBUSY" calendar component the property may be
   used to specify the interval of free time being requested. In a
   "VALARM" calendar component the property may be used to specify the
   delay period prior to repeating an alarm.
   Format Definition: The property is defined by the following notation:
     duration   = "DURATION" durparam ":" dur-value CRLF
                  ;consisting of a positive duration of time.

     durparam   = *(";" xparam)

Example: The following is an example of this property that specifies an interval of time of 1 hour and zero minutes and zero seconds:
     DURATION:PT1H0M0S

The following is an example of this property that specifies an interval of time of 15 minutes.
     DURATION:PT15M

4.8.2.6 Free/Busy Time

Property Name: FREEBUSY

   Purpose: The property defines one or more free or busy time
   intervals.
   Value Type: PERIOD. The date and time values MUST be in an UTC time
   format.
   Property Parameters: Non-standard or free/busy time type property
   parameters can be specified on this property.
   Conformance: The property can be specified in a "VFREEBUSY" calendar
   component.
   Property Parameter: "FBTYPE" and non-standard parameters can be
   specified on this property.
   Description: These time periods can be specified as either a start
   and end date-time or a start date-time and duration. The date and
   time MUST be a UTC time format.
   "FREEBUSY" properties within the "VFREEBUSY" calendar component
   SHOULD be sorted in ascending order, based on start time and then end
   time, with the earliest periods first.
   The "FREEBUSY" property can specify more than one value, separated by
   the COMMA character (US-ASCII decimal 44). In such cases, the
   "FREEBUSY" property values SHOULD all be of the same "FBTYPE"
   property parameter type (e.g., all values of a particular "FBTYPE"
   listed together in a single property).
   Format Definition: The property is defined by the following notation:
     freebusy   = "FREEBUSY" fbparam ":" fbvalue
                  CRLF

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

                (";" fbtypeparam) /

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

                (";" xparam)

                )

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

Example: The following are some examples of this property:
     FREEBUSY;FBTYPE=BUSY-UNAVAILABLE:19970308T160000Z/PT8H30M

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

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

4.8.2.7 Time Transparency

Property Name: TRANSP

   Purpose: This property defines whether an event is transparent or not
   to busy time searches.
   Value Type: TEXT
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property can be specified once in a "VEVENT"
   calendar component.
   Description: Time Transparency is the characteristic of an event that
   determines whether it appears to consume time on a calendar. Events
   that consume actual time for the individual or resource associated
   with the calendar SHOULD be recorded as OPAQUE, allowing them to be
   detected by free-busy time searches. Other events, which do not take
   up the individual's (or resource's) time SHOULD be recorded as
   TRANSPARENT, making them invisible to free-busy time searches.
   Format Definition: The property is specified by the following
   notation:
     transp     = "TRANSP" tranparam ":" transvalue CRLF

     tranparam  = *(";" xparam)

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

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

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

4.8.3 Time Zone Component Properties

The following properties specify time zone information in calendar components.


4.8.3.1 Time Zone Identifier

Property Name: TZID

   Purpose: This property specifies the text value that uniquely
   identifies the "VTIMEZONE" calendar component.
   Value Type: TEXT
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property MUST be specified in a "VTIMEZONE"
   calendar component.
   Description: This is the label by which a time zone calendar
   component is referenced by any iCalendar properties whose data type
   is either DATE-TIME or TIME and not intended to specify a UTC or a
   "floating" time. The presence of the SOLIDUS character (US-ASCII
   decimal 47) as a prefix, indicates that this TZID represents an
   unique ID in a globally defined time zone registry (when such
   registry is defined).
        Note: This document does not define a naming convention for time
        zone identifiers. Implementers may want to use the naming
        conventions defined in existing time zone specifications such as
        the public-domain Olson database [TZ]. The specification of
        globally unique time zone identifiers is not addressed by this
        document and is left for future study.

Format Definition: This property is defined by the following notation:
     tzid       = "TZID" tzidpropparam ":" [tzidprefix] text CRLF

     tzidpropparam      = *(";" xparam)

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

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

     TZID:California-Los_Angeles

The following is an example of a fictitious globally unique time zone identifier:
     TZID:/US-New_York-New_York

4.8.3.2 Time Zone Name

Property Name: TZNAME

   Purpose: This property specifies the customary designation for a time
   zone description.
   Value Type: TEXT
   Property Parameters: Non-standard and language property parameters
   can be specified on this property.
   Conformance: This property can be specified in a "VTIMEZONE" calendar
   component.
   Description: This property may be specified in multiple languages; in
   order to provide for different language requirements.
   Format Definition: This property is defined by the following
   notation:
     tzname     = "TZNAME" tznparam ":" text CRLF

     tznparam   = *(

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

                (";" languageparam) /

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

                (";" xparam)

                )

Example: The following are example of this property:
     TZNAME:EST

The following is an example of this property when two different languages for the time zone name are specified:
     TZNAME;LANGUAGE=en:EST
     TZNAME;LANGUAGE=fr-CA:HNE

4.8.3.3 Time Zone Offset From

Property Name: TZOFFSETFROM

   Purpose: This property specifies the offset which is in use prior to
   this time zone observance.
   Value Type: UTC-OFFSET
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property MUST be specified in a "VTIMEZONE"
   calendar component.
   Description: This property specifies the offset which is in use prior
   to this time observance. It is used to calculate the absolute time at
   which the transition to a given observance takes place. This property
   MUST only be specified in a "VTIMEZONE" calendar component. A
   "VTIMEZONE" calendar component MUST include this property. The
   property value is a signed numeric indicating the number of hours and
   possibly minutes from UTC. Positive numbers represent time zones east
   of the prime meridian, or ahead of UTC. Negative numbers represent
   time zones west of the prime meridian, or behind UTC.
   Format Definition: The property is defined by the following notation:
     tzoffsetfrom       = "TZOFFSETFROM" frmparam ":" utc-offset
                          CRLF

     frmparam   = *(";" xparam)

Example: The following are examples of this property:
     TZOFFSETFROM:-0500

     TZOFFSETFROM:+1345

4.8.3.4 Time Zone Offset To

Property Name: TZOFFSETTO

   Purpose: This property specifies the offset which is in use in this
   time zone observance.
   Value Type: UTC-OFFSET
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property MUST be specified in a "VTIMEZONE"
   calendar component.
   Description: This property specifies the offset which is in use in
   this time zone observance. It is used to calculate the absolute time
   for the new observance. The property value is a signed numeric
   indicating the number of hours and possibly minutes from UTC.
   Positive numbers represent time zones east of the prime meridian, or
   ahead of UTC. Negative numbers represent time zones west of the prime
   meridian, or behind UTC.
   Format Definition: The property is defined by the following notation:
     tzoffsetto = "TZOFFSETTO" toparam ":" utc-offset CRLF

     toparam    = *(";" xparam)

Example: The following are examples of this property:
     TZOFFSETTO:-0400

     TZOFFSETTO:+1245

4.8.3.5 Time Zone URL

Property Name: TZURL

   Purpose: The TZURL provides a means for a VTIMEZONE component to
   point to a network location that can be used to retrieve an up-to-
   date version of itself.
   Value Type: URI
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property can be specified in a "VTIMEZONE" calendar
   component.
   Description: The TZURL provides a means for a VTIMEZONE component to
   point to a network location that can be used to retrieve an up-to-
   date version of itself. This provides a hook to handle changes
   government bodies impose upon time zone definitions. Retrieval of
   this resource results in an iCalendar object containing a single
   VTIMEZONE component and a METHOD property set to PUBLISH.
   Format Definition: The property is defined by the following notation:
     tzurl      = "TZURL" tzurlparam ":" uri CRLF

     tzurlparam = *(";" xparam)

Example: The following is an example of this property:
     TZURL:http://timezones.r.us.net/tz/US-California-Los_Angeles

4.8.4 Relationship Component Properties

The following properties specify relationship information in calendar components.


4.8.4.1 Attendee

Property Name: ATTENDEE

   Purpose: The property defines an "Attendee" within a calendar
   component.
   Value Type: CAL-ADDRESS
   Property Parameters: Non-standard, language, calendar user type,
   group or list membership, participation role, participation status,
   RSVP expectation, delegatee, delegator, sent by, common name or
   directory entry reference property parameters can be specified on
   this property.
   Conformance: This property MUST be specified in an iCalendar object
   that specifies a group scheduled calendar entity. This property MUST
   NOT be specified in an iCalendar object when publishing the calendar
   information (e.g., NOT in an iCalendar object that specifies the
   publication of a calendar user's busy time, event, to-do or journal).
   This property is not specified in an iCalendar object that specifies
   only a time zone definition or that defines calendar entities that
   are not group scheduled entities, but are entities only on a single
   user's calendar.
   Description: The property MUST only be specified within calendar
   components to specify participants, non-participants and the chair of
   a group scheduled calendar entity. The property is specified within
   an "EMAIL" category of the "VALARM" calendar component to specify an
   email address that is to receive the email type of iCalendar alarm.
   The property parameter CN is for the common or displayable name
   associated with the calendar address; ROLE, for the intended role
   that the attendee will have in the calendar component; PARTSTAT, for
   the status of the attendee's participation; RSVP, for indicating
   whether the favor of a reply is requested; CUTYPE, to indicate the
   type of calendar user; MEMBER, to indicate the groups that the
   attendee belongs to; DELEGATED-TO, to indicate the calendar users
   that the original request was delegated to; and DELEGATED-FROM, to
   indicate whom the request was delegated from; SENT-BY, to indicate
   whom is acting on behalf of the ATTENDEE; and DIR, to indicate the
   URI that points to the directory information corresponding to the
   attendee. These property parameters can be specified on an "ATTENDEE"
   property in either a "VEVENT", "VTODO" or "VJOURNAL" calendar
   component. They MUST not be specified in an "ATTENDEE" property in a
   "VFREEBUSY" or "VALARM" calendar component. If the LANGUAGE property
   parameter is specified, the identified language applies to the CN
   parameter.
   A recipient delegated a request MUST inherit the RSVP and ROLE values
   from the attendee that delegated the request to them.
   Multiple attendees can be specified by including multiple "ATTENDEE"
   properties within the calendar component.
   Format Definition: The property is defined by the following notation:
     attendee   = "ATTENDEE" attparam ":" cal-address CRLF

     attparam   = *(

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

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

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

                (";" xparam)

                )

Example: The following are examples of this property's use for a to- do:
     ORGANIZER:MAILTO:jsmith@host1.com
     ATTENDEE;MEMBER="MAILTO:DEV-GROUP@host2.com":
      MAILTO:joecool@host2.com
     ATTENDEE;DELEGATED-FROM="MAILTO:immud@host3.com":
      MAILTO:ildoit@host1.com

The following is an example of this property used for specifying multiple attendees to an event:
     ORGANIZER:MAILTO:jsmith@host1.com
     ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=TENTATIVE;CN=Henry Cabot
      :MAILTO:hcabot@host2.com
     ATTENDEE;ROLE=REQ-PARTICIPANT;DELEGATED-FROM="MAILTO:bob@host.com"
      ;PARTSTAT=ACCEPTED;CN=Jane Doe:MAILTO:jdoe@host1.com

The following is an example of this property with a URI to the directory information associated with the attendee:
     ATTENDEE;CN=John Smith;DIR="ldap://host.com:6666/o=eDABC%
      20Industries,c=3DUS??(cn=3DBJim%20Dolittle)":MAILTO:jimdo@
      host1.com

The following is an example of this property with "delegatee" and "delegator" information for an event:
     ORGANIZER;CN=John Smith:MAILTO:jsmith@host.com
     ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=TENTATIVE;DELEGATED-FROM=
      "MAILTO:iamboss@host2.com";CN=Henry Cabot:MAILTO:hcabot@
      host2.com
     ATTENDEE;ROLE=NON-PARTICIPANT;PARTSTAT=DELEGATED;DELEGATED-TO=
      "MAILTO:hcabot@host2.com";CN=The Big Cheese:MAILTO:iamboss
      @host2.com
     ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=ACCEPTED;CN=Jane Doe
      :MAILTO:jdoe@host1.com

Example: The following is an example of this property's use when another calendar user is acting on behalf of the "Attendee":
     ATTENDEE;SENT-BY=MAILTO:jan_doe@host1.com;CN=John Smith:MAILTO:
      jsmith@host1.com

4.8.4.2 Contact

Property Name: CONTACT

   Purpose: The property is used to represent contact information or
   alternately a reference to contact information associated with the
   calendar component.
   Value Type: TEXT
   Property Parameters: Non-standard, alternate text representation and
   language property parameters can be specified on this property.
   Conformance: The property can be specified in a "VEVENT", "VTODO",
   "VJOURNAL" or "VFREEBUSY" calendar component.
   Description: The property value consists of textual contact
   information. An alternative representation for the property value can
   also be specified that refers to a URI pointing to an alternate form,
   such as a vCard [RFC 2426], for the contact information.
   Format Definition: The property is defined by the following notation:
     contact    = "CONTACT" contparam ":" text CRLF

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

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

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

                (";" xparam)

                )

Example: The following is an example of this property referencing textual contact information:
     CONTACT:Jim Dolittle\, ABC Industries\, +1-919-555-1234

The following is an example of this property with an alternate representation of a LDAP URI to a directory entry containing the contact information:
     CONTACT;ALTREP="ldap://host.com:6666/o=3DABC%20Industries\,
      c=3DUS??(cn=3DBJim%20Dolittle)":Jim Dolittle\, ABC Industries\,
      +1-919-555-1234

The following is an example of this property with an alternate representation of a MIME body part containing the contact information, such as a vCard [RFC 2426] embedded in a [MIME-DIR] content-type:
     CONTACT;ALTREP="CID=<part3.msg970930T083000SILVER@host.com>":Jim
       Dolittle\, ABC Industries\, +1-919-555-1234

The following is an example of this property referencing a network resource, such as a vCard [RFC 2426] object containing the contact information:
     CONTACT;ALTREP="http://host.com/pdi/jdoe.vcf":Jim
       Dolittle\, ABC Industries\, +1-919-555-1234

4.8.4.3 Organizer

Property Name: ORGANIZER

   Purpose: The property defines the organizer for a calendar component.
   Value Type: CAL-ADDRESS
   Property Parameters: Non-standard, language, common name, directory
   entry reference, sent by property parameters can be specified on this
   property.
   Conformance: This property MUST be specified in an iCalendar object
   that specifies a group scheduled calendar entity. This property MUST
   be specified in an iCalendar object that specifies the publication of
   a calendar user's busy time. This property MUST NOT be specified in
   an iCalendar object that specifies only a time zone definition or
   that defines calendar entities that are not group scheduled entities,
   but are entities only on a single user's calendar.
   Description: The property is specified within the "VEVENT", "VTODO",
   "VJOURNAL calendar components to specify the organizer of a group
   scheduled calendar entity. The property is specified within the
   "VFREEBUSY" calendar component to specify the calendar user
   requesting the free or busy time. When publishing a "VFREEBUSY"
   calendar component, the property is used to specify the calendar that
   the published busy time came from.
   The property has the property parameters CN, for specifying the
   common or display name associated with the "Organizer", DIR, for
   specifying a pointer to the directory information associated with the
   "Organizer", SENT-BY, for specifying another calendar user that is
   acting on behalf of the "Organizer". The non-standard parameters may
   also be specified on this property. If the LANGUAGE property
   parameter is specified, the identified language applies to the CN
   parameter value.
   Format Definition: The property is defined by the following notation:
     organizer  = "ORGANIZER" orgparam ":"
                  cal-address CRLF

     orgparam   = *(

                ; the following are optional,

                ; but MUST NOT occur more than once

                (";" cnparam) / (";" dirparam) / (";" sentbyparam) /
                (";" languageparam) /

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

                (";" xparam)

                )

Example: The following is an example of this property:
     ORGANIZER;CN=John Smith:MAILTO:jsmith@host1.com

The following is an example of this property with a pointer to the directory information associated with the organizer:
     ORGANIZER;CN=JohnSmith;DIR="ldap://host.com:6666/o=3DDC%20Associ
      ates,c=3DUS??(cn=3DJohn%20Smith)":MAILTO:jsmith@host1.com

The following is an example of this property used by another calendar user who is acting on behalf of the organizer, with responses intended to be sent back to the organizer, not the other calendar user:
     ORGANIZER;SENT-BY="MAILTO:jane_doe@host.com":
      MAILTO:jsmith@host1.com

4.8.4.4 Recurrence ID

Property Name: RECURRENCE-ID

   Purpose: This property is used in conjunction with the "UID" and
   "SEQUENCE" property to identify a specific instance of a recurring
   "VEVENT", "VTODO" or "VJOURNAL" calendar component. The property
   value is the effective value of the "DTSTART" property of the
   recurrence instance.
   Value Type: The default value type for this property is DATE-TIME.
   The time format can be any of the valid forms defined for a DATE-TIME
   value type. See DATE-TIME value type definition for specific
   interpretations of the various forms. The value type can be set to
   DATE.
   Property Parameters: Non-standard property, value data type, time
   zone identifier and recurrence identifier range parameters can be
   specified on this property.
   Conformance: This property can be specified in an iCalendar object
   containing a recurring calendar component.
   Description: The full range of calendar components specified by a
   recurrence set is referenced by referring to just the "UID" property
   value corresponding to the calendar component. The "RECURRENCE-ID"
   property allows the reference to an individual instance within the
   recurrence set.
   If the value of the "DTSTART" property is a DATE type value, then the
   value MUST be the calendar date for the recurrence instance.
   The date/time value is set to the time when the original recurrence
   instance would occur; meaning that if the intent is to change a
   Friday meeting to Thursday, the date/time is still set to the
   original Friday meeting.
   The "RECURRENCE-ID" property is used in conjunction with the "UID"
   and "SEQUENCE" property to identify a particular instance of a
   recurring event, to-do or journal. For a given pair of "UID" and
   "SEQUENCE" property values, the "RECURRENCE-ID" value for a
   recurrence instance is fixed. When the definition of the recurrence
   set for a calendar component changes, and hence the "SEQUENCE"
   property value changes, the "RECURRENCE-ID" for a given recurrence
   instance might also change.The "RANGE" parameter is used to specify
   the effective range of recurrence instances from the instance
   specified by the "RECURRENCE-ID" property value. The default value
   for the range parameter is the single recurrence instance only. The
   value can also be "THISANDPRIOR" to indicate a range defined by the
   given recurrence instance and all prior instances or the value can be
   "THISANDFUTURE" to indicate a range defined by the given recurrence
   instance and all subsequent instances.
   Format Definition: The property is defined by the following notation:
     recurid    = "RECURRENCE-ID" ridparam ":" ridval CRLF

     ridparam   = *(

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

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

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

                (";" xparam)

                )

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

Example: The following are examples of this property:
     RECURRENCE-ID;VALUE=DATE:19960401

     RECURRENCE-ID;RANGE=THISANDFUTURE:19960120T120000Z

4.8.4.5 Related To

Property Name: RELATED-TO

   Purpose: The property is used to represent a relationship or
   reference between one calendar component and another.
   Value Type: TEXT
   Property Parameters: Non-standard and relationship type property
   parameters can be specified on this property.
   Conformance: The property can be specified one or more times in the
   "VEVENT", "VTODO" or "VJOURNAL" calendar components.
   Description: The property value consists of the persistent, globally
   unique identifier of another calendar component. This value would be
   represented in a calendar component by the "UID" property.
   By default, the property value points to another calendar component
   that has a PARENT relationship to the referencing object. The
   "RELTYPE" property parameter is used to either explicitly state the
   default PARENT relationship type to the referenced calendar component
   or to override the default PARENT relationship type and specify
   either a CHILD or SIBLING relationship. The PARENT relationship
   indicates that the calendar component is a subordinate of the
   referenced calendar component. The CHILD relationship indicates that
   the calendar component is a superior of the referenced calendar
   component. The SIBLING relationship indicates that the calendar
   component is a peer of the referenced calendar component.
   Changes to a calendar component referenced by this property can have
   an implicit impact on the related calendar component. For example, if
   a group event changes its start or end date or time, then the
   related, dependent events will need to have their start and end dates
   changed in a corresponding way. Similarly, if a PARENT calendar
   component is canceled or deleted, then there is an implied impact to
   the related CHILD calendar components. This property is intended only
   to provide information on the relationship of calendar components. It
   is up to the target calendar system to maintain any property
   implications of this relationship.
   Format Definition: The property is defined by the following notation:
     related    = "RELATED-TO" [relparam] ":" text CRLF

     relparam   = *(

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

                (";" reltypeparam) /

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

                (";" xparm)

                )

The following is an example of this property:
     RELATED-TO:<jsmith.part7.19960817T083000.xyzMail@host3.com>

     RELATED-TO:<19960401-080045-4000F192713-0052@host1.com>

4.8.4.6 Uniform Resource Locator

Property Name: URL

   Purpose: This property defines a Uniform Resource Locator (URL)
   associated with the iCalendar object.
   Value Type: URI
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property can be specified once in the "VEVENT",
   "VTODO", "VJOURNAL" or "VFREEBUSY" calendar components.
   Description: This property may be used in a calendar component to
   convey a location where a more dynamic rendition of the calendar
   information associated with the calendar component can be found. This
   memo does not attempt to standardize the form of the URI, nor the
   format of the resource pointed to by the property value. If the URL
   property and Content-Location MIME header are both specified, they
   MUST point to the same resource.
   Format Definition: The property is defined by the following notation:
     url        = "URL" urlparam ":" uri CRLF

     urlparam   = *(";" xparam)

Example: The following is an example of this property:
     URL:http://abc.com/pub/calendars/jsmith/mytime.ics

4.8.4.7 Unique Identifier

Property Name: UID

   Purpose: This property defines the persistent, globally unique
   identifier for the calendar component.
   Value Type: TEXT
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: The property MUST be specified in the "VEVENT", "VTODO",
   "VJOURNAL" or "VFREEBUSY" calendar components.
   Description: The UID itself MUST be a globally unique identifier. The
   generator of the identifier MUST guarantee that the identifier is
   unique. There are several algorithms that can be used to accomplish
   this. The identifier is RECOMMENDED to be the identical syntax to the
   [RFC 822] addr-spec. A good method to assure uniqueness is to put the
   domain name or a domain literal IP address of the host on which the
   identifier was created on the right hand side of the "@", and on the
   left hand side, put a combination of the current calendar date and
   time of day (i.e., formatted in as a DATE-TIME value) along with some
   other currently unique (perhaps sequential) identifier available on
   the system (for example, a process id number). Using a date/time
   value on the left hand side and a domain name or domain literal on
   the right hand side makes it possible to guarantee uniqueness since
   no two hosts should be using the same domain name or IP address at
   the same time. Though other algorithms will work, it is RECOMMENDED
   that the right hand side contain some domain identifier (either of
   the host itself or otherwise) such that the generator of the message
   identifier can guarantee the uniqueness of the left hand side within
   the scope of that domain.
   This is the method for correlating scheduling messages with the
   referenced "VEVENT", "VTODO", or "VJOURNAL" calendar component.
   The full range of calendar components specified by a recurrence set
   is referenced by referring to just the "UID" property value
   corresponding to the calendar component. The "RECURRENCE-ID" property
   allows the reference to an individual instance within the recurrence
   set.
   This property is an important method for group scheduling
   applications to match requests with later replies, modifications or
   deletion requests. Calendaring and scheduling applications MUST
   generate this property in "VEVENT", "VTODO" and "VJOURNAL" calendar
   components to assure interoperability with other group scheduling
   applications. This identifier is created by the calendar system that
   generates an iCalendar object.
   Implementations MUST be able to receive and persist values of at
   least 255 characters for this property.
   Format Definition: The property is defined by the following notation:
     uid        = "UID" uidparam ":" text CRLF

     uidparam   = *(";" xparam)

Example: The following is an example of this property:
     UID:19960401T080045Z-4000F192713-0052@host1.com

4.8.5 Recurrence Component Properties

The following properties specify recurrence information in calendar components.


4.8.5.1 Exception Date/Times

Property Name: EXDATE

   Purpose: This property defines the list of date/time exceptions for a
   recurring calendar component.
   Value Type: The default value type for this property is DATE-TIME.
   The value type can be set to DATE.
   Property Parameters: Non-standard, value data type and time zone
   identifier property parameters can be specified on this property.
   Conformance: This property can be specified in an iCalendar object
   that includes a recurring calendar component.
   Description: The exception dates, if specified, are used in computing
   the recurrence set. The recurrence set is the complete set of
   recurrence instances for a calendar component. The recurrence set is
   generated by considering the initial "DTSTART" property along with
   the "RRULE", "RDATE", "EXDATE" and "EXRULE" properties contained
   within the iCalendar object. The "DTSTART" property defines the first
   instance in the recurrence set. Multiple instances of the "RRULE" and
   "EXRULE" properties can also be specified to define more
   sophisticated recurrence sets. The final recurrence set is generated
   by gathering all of the start date-times generated by any of the
   specified "RRULE" and "RDATE" properties, and then excluding any
   start date and times which fall within the union of start date and
   times generated by any specified "EXRULE" and "EXDATE" properties.
   This implies that start date and times within exclusion related
   properties (i.e., "EXDATE" and "EXRULE") take precedence over those
   specified by inclusion properties (i.e., "RDATE" and "RRULE"). Where
   duplicate instances are generated by the "RRULE" and "RDATE"
   properties, only one recurrence is considered. Duplicate instances
   are ignored.
   The "EXDATE" property can be used to exclude the value specified in
   "DTSTART". However, in such cases the original "DTSTART" date MUST
   still be maintained by the calendaring and scheduling system because
   the original "DTSTART" value has inherent usage dependencies by other
   properties such as the "RECURRENCE-ID".
   Format Definition: The property is defined by the following notation:
     exdate     = "EXDATE" exdtparam ":" exdtval *("," exdtval) CRLF

     exdtparam  = *(

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

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

                (";" tzidparam) /

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

                (";" xparam)

                )

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

Example: The following is an example of this property:
     EXDATE:19960402T010000Z,19960403T010000Z,19960404T010000Z

4.8.5.2 Exception Rule

Property Name: EXRULE

   Purpose: This property defines a rule or repeating pattern for an
   exception to a recurrence set.
   Value Type: RECUR
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property can be specified in "VEVENT", "VTODO" or
   "VJOURNAL" calendar components.
   Description: The exception rule, if specified, is used in computing
   the recurrence set. The recurrence set is the complete set of
   recurrence instances for a calendar component. The recurrence set is
   generated by considering the initial "DTSTART" property along with
   the "RRULE", "RDATE", "EXDATE" and "EXRULE" properties contained
   within the iCalendar object. The "DTSTART" defines the first instance
   in the recurrence set. Multiple instances of the "RRULE" and "EXRULE"
   properties can also be specified to define more sophisticated
   recurrence sets. The final recurrence set is generated by gathering
   all of the start date-times generated by any of the specified "RRULE"
   and "RDATE" properties, and excluding any start date and times which
   fall within the union of start date and times generated by any
   specified "EXRULE" and "EXDATE" properties. This implies that start
   date and times within exclusion related properties (i.e., "EXDATE"
   and "EXRULE") take precedence over those specified by inclusion
   properties (i.e., "RDATE" and "RRULE"). Where duplicate instances are
   generated by the "RRULE" and "RDATE" properties, only one recurrence
   is considered. Duplicate instances are ignored.
   The "EXRULE" property can be used to exclude the value specified in
   "DTSTART". However, in such cases the original "DTSTART" date MUST
   still be maintained by the calendaring and scheduling system because
   the original "DTSTART" value has inherent usage dependencies by other
   properties such as the "RECURRENCE-ID".
   Format Definition: The property is defined by the following notation:
     exrule     = "EXRULE" exrparam ":" recur CRLF

     exrparam   = *(";" xparam)

Example: The following are examples of this property. Except every other week, on Tuesday and Thursday for 4 occurrences:
     EXRULE:FREQ=WEEKLY;COUNT=4;INTERVAL=2;BYDAY=TU,TH

Except daily for 10 occurrences:
     EXRULE:FREQ=DAILY;COUNT=10

Except yearly in June and July for 8 occurrences:
     EXRULE:FREQ=YEARLY;COUNT=8;BYMONTH=6,7

4.8.5.3 Recurrence Date/Times

Property Name: RDATE

   Purpose: This property defines the list of date/times for a
   recurrence set.
   Value Type: The default value type for this property is DATE-TIME.
   The value type can be set to DATE or PERIOD.
   Property Parameters: Non-standard, value data type and time zone
   identifier property parameters can be specified on this property.
   Conformance: The property can be specified in "VEVENT", "VTODO",
   "VJOURNAL" or "VTIMEZONE" calendar components.
   Description: This property can appear along with the "RRULE" property
   to define an aggregate set of repeating occurrences. When they both
   appear in an iCalendar object, the recurring events are defined by
   the union of occurrences defined by both the "RDATE" and "RRULE".
   The recurrence dates, if specified, are used in computing the
   recurrence set. The recurrence set is the complete set of recurrence
   instances for a calendar component. The recurrence set is generated
   by considering the initial "DTSTART" property along with the "RRULE",
   "RDATE", "EXDATE" and "EXRULE" properties contained within the
   iCalendar object. The "DTSTART" property defines the first instance
   in the recurrence set. Multiple instances of the "RRULE" and "EXRULE"
   properties can also be specified to define more sophisticated
   recurrence sets. The final recurrence set is generated by gathering
   all of the start date/times generated by any of the specified "RRULE"
   and "RDATE" properties, and excluding any start date/times which fall
   within the union of start date/times generated by any specified
   "EXRULE" and "EXDATE" properties. This implies that start date/times
   within exclusion related properties (i.e., "EXDATE" and "EXRULE")
   take precedence over those specified by inclusion properties (i.e.,
   "RDATE" and "RRULE"). Where duplicate instances are generated by the
   "RRULE" and "RDATE" properties, only one recurrence is considered.
   Duplicate instances are ignored.
   Format Definition: The property is defined by the following notation:
     rdate      = "RDATE" rdtparam ":" rdtval *("," rdtval) CRLF

     rdtparam   = *(

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

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

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

                (";" xparam)

                )

     rdtval     = date-time / date / period
     ;Value MUST match value type

Example: The following are examples of this property:
     RDATE:19970714T123000Z

     RDATE;TZID=US-EASTERN:19970714T083000

     RDATE;VALUE=PERIOD:19960403T020000Z/19960403T040000Z,
      19960404T010000Z/PT3H

     RDATE;VALUE=DATE:19970101,19970120,19970217,19970421
      19970526,19970704,19970901,19971014,19971128,19971129,19971225

4.8.5.4 Recurrence Rule

Property Name: RRULE

   Purpose: This property defines a rule or repeating pattern for
   recurring events, to-dos, or time zone definitions.
   Value Type: RECUR
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property can be specified one or more times in
   recurring "VEVENT", "VTODO" and "VJOURNAL" calendar components. It
   can also be specified once in each STANDARD or DAYLIGHT sub-component
   of the "VTIMEZONE" calendar component.
   Description: The recurrence rule, if specified, is used in computing
   the recurrence set. The recurrence set is the complete set of
   recurrence instances for a calendar component. The recurrence set is
   generated by considering the initial "DTSTART" property along with
   the "RRULE", "RDATE", "EXDATE" and "EXRULE" properties contained
   within the iCalendar object. The "DTSTART" property defines the first
   instance in the recurrence set. Multiple instances of the "RRULE" and
   "EXRULE" properties can also be specified to define more
   sophisticated recurrence sets. The final recurrence set is generated
   by gathering all of the start date/times generated by any of the
   specified "RRULE" and "RDATE" properties, and excluding any start
   date/times which fall within the union of start date/times generated
   by any specified "EXRULE" and "EXDATE" properties. This implies that
   start date/times within exclusion related properties (i.e., "EXDATE"
   and "EXRULE") take precedence over those specified by inclusion
   properties (i.e., "RDATE" and "RRULE"). Where duplicate instances are
   generated by the "RRULE" and "RDATE" properties, only one recurrence
   is considered. Duplicate instances are ignored.
   The "DTSTART" and "DTEND" property pair or "DTSTART" and "DURATION"
   property pair, specified within the iCalendar object defines the
   first instance of the recurrence. When used with a recurrence rule,
   the "DTSTART" and "DTEND" properties MUST be specified in local time
   and the appropriate set of "VTIMEZONE" calendar components MUST be
   included. For detail on the usage of the "VTIMEZONE" calendar
   component, see the "VTIMEZONE" calendar component definition.
   Any duration associated with the iCalendar object applies to all
   members of the generated recurrence set. Any modified duration for
   specific recurrences MUST be explicitly specified using the "RDATE"
   property.
   Format Definition: This property is defined by the following
   notation:
     rrule      = "RRULE" rrulparam ":" recur CRLF

     rrulparam  = *(";" xparam)

Example: All examples assume the Eastern United States time zone.
   Daily for 10 occurrences:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=DAILY;COUNT=10

     ==> (1997 9:00 AM EDT)September 2-11

Daily until December 24, 1997:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=DAILY;UNTIL=19971224T000000Z

     ==> (1997 9:00 AM EDT)September 2-30;October 1-25
         (1997 9:00 AM EST)October 26-31;November 1-30;December 1-23

Every other day - forever:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=DAILY;INTERVAL=2
     ==> (1997 9:00 AM EDT)September2,4,6,8...24,26,28,30;
          October 2,4,6...20,22,24
         (1997 9:00 AM EST)October 26,28,30;November 1,3,5,7...25,27,29;
          Dec 1,3,...

Every 10 days, 5 occurrences:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=DAILY;INTERVAL=10;COUNT=5

     ==> (1997 9:00 AM EDT)September 2,12,22;October 2,12

Everyday in January, for 3 years:
     DTSTART;TZID=US-Eastern:19980101T090000
     RRULE:FREQ=YEARLY;UNTIL=20000131T090000Z;
      BYMONTH=1;BYDAY=SU,MO,TU,WE,TH,FR,SA
     or
     RRULE:FREQ=DAILY;UNTIL=20000131T090000Z;BYMONTH=1

     ==> (1998 9:00 AM EDT)January 1-31
         (1999 9:00 AM EDT)January 1-31
         (2000 9:00 AM EDT)January 1-31

Weekly for 10 occurrences
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=WEEKLY;COUNT=10

     ==> (1997 9:00 AM EDT)September 2,9,16,23,30;October 7,14,21
         (1997 9:00 AM EST)October 28;November 4

Weekly until December 24, 1997
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=WEEKLY;UNTIL=19971224T000000Z

     ==> (1997 9:00 AM EDT)September 2,9,16,23,30;October 7,14,21
         (1997 9:00 AM EST)October 28;November 4,11,18,25;
                           December 2,9,16,23
   Every other week - forever:

     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;WKST=SU

     ==> (1997 9:00 AM EDT)September 2,16,30;October 14
         (1997 9:00 AM EST)October 28;November 11,25;December 9,23
         (1998 9:00 AM EST)January 6,20;February
     ...

Weekly on Tuesday and Thursday for 5 weeks:
    DTSTART;TZID=US-Eastern:19970902T090000
    RRULE:FREQ=WEEKLY;UNTIL=19971007T000000Z;WKST=SU;BYDAY=TU,TH
    or
    RRULE:FREQ=WEEKLY;COUNT=10;WKST=SU;BYDAY=TU,TH

    ==> (1997 9:00 AM EDT)September 2,4,9,11,16,18,23,25,30;October 2

Every other week on Monday, Wednesday and Friday until December 24, 1997, but starting on Tuesday, September 2, 1997:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;UNTIL=19971224T000000Z;WKST=SU;
      BYDAY=MO,WE,FR
     ==> (1997 9:00 AM EDT)September 2,3,5,15,17,19,29;October
     1,3,13,15,17
         (1997 9:00 AM EST)October 27,29,31;November 10,12,14,24,26,28;
                           December 8,10,12,22

Every other week on Tuesday and Thursday, for 8 occurrences:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=8;WKST=SU;BYDAY=TU,TH

     ==> (1997 9:00 AM EDT)September 2,4,16,18,30;October 2,14,16

Monthly on the 1st Friday for ten occurrences:
     DTSTART;TZID=US-Eastern:19970905T090000
     RRULE:FREQ=MONTHLY;COUNT=10;BYDAY=1FR

     ==> (1997 9:00 AM EDT)September 5;October 3
         (1997 9:00 AM EST)November 7;Dec 5
         (1998 9:00 AM EST)January 2;February 6;March 6;April 3
         (1998 9:00 AM EDT)May 1;June 5

Monthly on the 1st Friday until December 24, 1997:
     DTSTART;TZID=US-Eastern:19970905T090000
     RRULE:FREQ=MONTHLY;UNTIL=19971224T000000Z;BYDAY=1FR

     ==> (1997 9:00 AM EDT)September 5;October 3
         (1997 9:00 AM EST)November 7;December 5

Every other month on the 1st and last Sunday of the month for 10 occurrences:
     DTSTART;TZID=US-Eastern:19970907T090000
     RRULE:FREQ=MONTHLY;INTERVAL=2;COUNT=10;BYDAY=1SU,-1SU

     ==> (1997 9:00 AM EDT)September 7,28
         (1997 9:00 AM EST)November 2,30

         (1998 9:00 AM EST)January 4,25;March 1,29
         (1998 9:00 AM EDT)May 3,31

Monthly on the second to last Monday of the month for 6 months:
     DTSTART;TZID=US-Eastern:19970922T090000
     RRULE:FREQ=MONTHLY;COUNT=6;BYDAY=-2MO

     ==> (1997 9:00 AM EDT)September 22;October 20
         (1997 9:00 AM EST)November 17;December 22
         (1998 9:00 AM EST)January 19;February 16

Monthly on the third to the last day of the month, forever:
     DTSTART;TZID=US-Eastern:19970928T090000
     RRULE:FREQ=MONTHLY;BYMONTHDAY=-3

     ==> (1997 9:00 AM EDT)September 28
         (1997 9:00 AM EST)October 29;November 28;December 29
         (1998 9:00 AM EST)January 29;February 26
     ...

Monthly on the 2nd and 15th of the month for 10 occurrences:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=MONTHLY;COUNT=10;BYMONTHDAY=2,15

     ==> (1997 9:00 AM EDT)September 2,15;October 2,15
         (1997 9:00 AM EST)November 2,15;December 2,15
         (1998 9:00 AM EST)January 2,15

Monthly on the first and last day of the month for 10 occurrences:
     DTSTART;TZID=US-Eastern:19970930T090000
     RRULE:FREQ=MONTHLY;COUNT=10;BYMONTHDAY=1,-1

     ==> (1997 9:00 AM EDT)September 30;October 1
         (1997 9:00 AM EST)October 31;November 1,30;December 1,31
         (1998 9:00 AM EST)January 1,31;February 1

Every 18 months on the 10th thru 15th of the month for 10 occurrences:
     DTSTART;TZID=US-Eastern:19970910T090000
     RRULE:FREQ=MONTHLY;INTERVAL=18;COUNT=10;BYMONTHDAY=10,11,12,13,14,
      15

     ==> (1997 9:00 AM EDT)September 10,11,12,13,14,15

         (1999 9:00 AM EST)March 10,11,12,13

Every Tuesday, every other month:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=MONTHLY;INTERVAL=2;BYDAY=TU

     ==> (1997 9:00 AM EDT)September 2,9,16,23,30
         (1997 9:00 AM EST)November 4,11,18,25
         (1998 9:00 AM EST)January 6,13,20,27;March 3,10,17,24,31
     ...

Yearly in June and July for 10 occurrences:
     DTSTART;TZID=US-Eastern:19970610T090000
     RRULE:FREQ=YEARLY;COUNT=10;BYMONTH=6,7
     ==> (1997 9:00 AM EDT)June 10;July 10
         (1998 9:00 AM EDT)June 10;July 10
         (1999 9:00 AM EDT)June 10;July 10
         (2000 9:00 AM EDT)June 10;July 10
         (2001 9:00 AM EDT)June 10;July 10
     Note: Since none of the BYDAY, BYMONTHDAY or BYYEARDAY components
     are specified, the day is gotten from DTSTART

Every other year on January, February, and March for 10 occurrences:
     DTSTART;TZID=US-Eastern:19970310T090000
     RRULE:FREQ=YEARLY;INTERVAL=2;COUNT=10;BYMONTH=1,2,3

     ==> (1997 9:00 AM EST)March 10
         (1999 9:00 AM EST)January 10;February 10;March 10
         (2001 9:00 AM EST)January 10;February 10;March 10
         (2003 9:00 AM EST)January 10;February 10;March 10

Every 3rd year on the 1st, 100th and 200th day for 10 occurrences:
     DTSTART;TZID=US-Eastern:19970101T090000
     RRULE:FREQ=YEARLY;INTERVAL=3;COUNT=10;BYYEARDAY=1,100,200

     ==> (1997 9:00 AM EST)January 1
         (1997 9:00 AM EDT)April 10;July 19
         (2000 9:00 AM EST)January 1
         (2000 9:00 AM EDT)April 9;July 18
         (2003 9:00 AM EST)January 1
         (2003 9:00 AM EDT)April 10;July 19
         (2006 9:00 AM EST)January 1

Every 20th Monday of the year, forever:
     DTSTART;TZID=US-Eastern:19970519T090000
     RRULE:FREQ=YEARLY;BYDAY=20MO

     ==> (1997 9:00 AM EDT)May 19
         (1998 9:00 AM EDT)May 18
         (1999 9:00 AM EDT)May 17
     ...

Monday of week number 20 (where the default start of the week is Monday), forever:
     DTSTART;TZID=US-Eastern:19970512T090000
     RRULE:FREQ=YEARLY;BYWEEKNO=20;BYDAY=MO

     ==> (1997 9:00 AM EDT)May 12
         (1998 9:00 AM EDT)May 11
         (1999 9:00 AM EDT)May 17
     ...

Every Thursday in March, forever:
     DTSTART;TZID=US-Eastern:19970313T090000
     RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=TH

     ==> (1997 9:00 AM EST)March 13,20,27
         (1998 9:00 AM EST)March 5,12,19,26
         (1999 9:00 AM EST)March 4,11,18,25
     ...

Every Thursday, but only during June, July, and August, forever:
     DTSTART;TZID=US-Eastern:19970605T090000
     RRULE:FREQ=YEARLY;BYDAY=TH;BYMONTH=6,7,8

     ==> (1997 9:00 AM EDT)June 5,12,19,26;July 3,10,17,24,31;
                       August 7,14,21,28
         (1998 9:00 AM EDT)June 4,11,18,25;July 2,9,16,23,30;
                       August 6,13,20,27
         (1999 9:00 AM EDT)June 3,10,17,24;July 1,8,15,22,29;
                       August 5,12,19,26
     ...

Every Friday the 13th, forever:
     DTSTART;TZID=US-Eastern:19970902T090000
     EXDATE;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=MONTHLY;BYDAY=FR;BYMONTHDAY=13

     ==> (1998 9:00 AM EST)February 13;March 13;November 13
         (1999 9:00 AM EDT)August 13
         (2000 9:00 AM EDT)October 13
     ...

The first Saturday that follows the first Sunday of the month, forever:
     DTSTART;TZID=US-Eastern:19970913T090000
     RRULE:FREQ=MONTHLY;BYDAY=SA;BYMONTHDAY=7,8,9,10,11,12,13

     ==> (1997 9:00 AM EDT)September 13;October 11
         (1997 9:00 AM EST)November 8;December 13
         (1998 9:00 AM EST)January 10;February 7;March 7
         (1998 9:00 AM EDT)April 11;May 9;June 13...
     ...

Every four years, the first Tuesday after a Monday in November, forever (U.S. Presidential Election day):
     DTSTART;TZID=US-Eastern:19961105T090000
     RRULE:FREQ=YEARLY;INTERVAL=4;BYMONTH=11;BYDAY=TU;BYMONTHDAY=2,3,4,
      5,6,7,8

     ==> (1996 9:00 AM EST)November 5
         (2000 9:00 AM EST)November 7
         (2004 9:00 AM EST)November 2
     ...

The 3rd instance into the month of one of Tuesday, Wednesday or Thursday, for the next 3 months:
     DTSTART;TZID=US-Eastern:19970904T090000
     RRULE:FREQ=MONTHLY;COUNT=3;BYDAY=TU,WE,TH;BYSETPOS=3

     ==> (1997 9:00 AM EDT)September 4;October 7
         (1997 9:00 AM EST)November 6

The 2nd to last weekday of the month:
     DTSTART;TZID=US-Eastern:19970929T090000
     RRULE:FREQ=MONTHLY;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=-2

     ==> (1997 9:00 AM EDT)September 29
         (1997 9:00 AM EST)October 30;November 27;December 30
         (1998 9:00 AM EST)January 29;February 26;March 30
     ...

Every 3 hours from 9:00 AM to 5:00 PM on a specific day:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=HOURLY;INTERVAL=3;UNTIL=19970902T170000Z

     ==> (September 2, 1997 EDT)09:00,12:00,15:00

Every 15 minutes for 6 occurrences:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=MINUTELY;INTERVAL=15;COUNT=6

     ==> (September 2, 1997 EDT)09:00,09:15,09:30,09:45,10:00,10:15

Every hour and a half for 4 occurrences:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=MINUTELY;INTERVAL=90;COUNT=4

     ==> (September 2, 1997 EDT)09:00,10:30;12:00;13:30

Every 20 minutes from 9:00 AM to 4:40 PM every day:
     DTSTART;TZID=US-Eastern:19970902T090000
     RRULE:FREQ=DAILY;BYHOUR=9,10,11,12,13,14,15,16;BYMINUTE=0,20,40
     or
     RRULE:FREQ=MINUTELY;INTERVAL=20;BYHOUR=9,10,11,12,13,14,15,16

     ==> (September 2, 1997 EDT)9:00,9:20,9:40,10:00,10:20,
                                ... 16:00,16:20,16:40
         (September 3, 1997 EDT)9:00,9:20,9:40,10:00,10:20,
                               ...16:00,16:20,16:40
     ...

An example where the days generated makes a difference because of WKST:
     DTSTART;TZID=US-Eastern:19970805T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=4;BYDAY=TU,SU;WKST=MO

     ==> (1997 EDT)Aug 5,10,19,24

     changing only WKST from MO to SU, yields different results...

     DTSTART;TZID=US-Eastern:19970805T090000
     RRULE:FREQ=WEEKLY;INTERVAL=2;COUNT=4;BYDAY=TU,SU;WKST=SU
     ==> (1997 EDT)August 5,17,19,31

4.8.6 Alarm Component Properties

The following properties specify alarm information in calendar components.


4.8.6.1 Action

Property Name: ACTION

   Purpose: This property defines the action to be invoked when an alarm
   is triggered.
   Value Type: TEXT
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property MUST be specified once in a "VALARM"
   calendar component.
   Description: Each "VALARM" calendar component has a particular type
   of action associated with it. This property specifies the type of
   action
   Format Definition: The property is defined by the following notation:
     action     = "ACTION" actionparam ":" actionvalue CRLF

     actionparam        = *(";" xparam)

     actionvalue        = "AUDIO" / "DISPLAY" / "EMAIL" / "PROCEDURE"
                        / iana-token / x-name

Example: The following are examples of this property in a "VALARM" calendar component:
     ACTION:AUDIO

     ACTION:DISPLAY

     ACTION:PROCEDURE

4.8.6.2 Repeat Count

Property Name: REPEAT

   Purpose: This property defines the number of time the alarm should be
   repeated, after the initial trigger.
   Value Type: INTEGER
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property can be specified in a "VALARM" calendar
   component.
   Description: If the alarm triggers more than once, then this property
   MUST be specified along with the "DURATION" property.
   Format Definition: The property is defined by the following notation:
     repeatcnt  = "REPEAT" repparam ":" integer CRLF
     ;Default is "0", zero.

     repparam   = *(";" xparam)

Example: The following is an example of this property for an alarm that repeats 4 additional times with a 5 minute delay after the initial triggering of the alarm:
     REPEAT:4
     DURATION:PT5M

4.8.6.3 Trigger

Property Name: TRIGGER

   Purpose: This property specifies when an alarm will trigger.
   Value Type: The default value type is DURATION. The value type can be
   set to a DATE-TIME value type, in which case the value MUST specify a
   UTC formatted DATE-TIME value.
   Property Parameters: Non-standard, value data type, time zone
   identifier or trigger relationship property parameters can be
   specified on this property. The trigger relationship property
   parameter MUST only be specified when the value type is DURATION.
   Conformance: This property MUST be specified in the "VALARM" calendar
   component.
   Description: Within the "VALARM" calendar component, this property
   defines when the alarm will trigger. The default value type is
   DURATION, specifying a relative time for the trigger of the alarm.
   The default duration is relative to the start of an event or to-do
   that the alarm is associated with. The duration can be explicitly set
   to trigger from either the end or the start of the associated event
   or to-do with the "RELATED" parameter. A value of START will set the
   alarm to trigger off the start of the associated event or to-do. A
   value of END will set the alarm to trigger off the end of the
   associated event or to-do.
   Either a positive or negative duration may be specified for the
   "TRIGGER" property. An alarm with a positive duration is triggered
   after the associated start or end of the event or to-do. An alarm
   with a negative duration is triggered before the associated start or
   end of the event or to-do.
   The "RELATED" property parameter is not valid if the value type of
   the property is set to DATE-TIME (i.e., for an absolute date and time
   alarm trigger). If a value type of DATE-TIME is specified, then the
   property value MUST be specified in the UTC time format. If an
   absolute trigger is specified on an alarm for a recurring event or
   to-do, then the alarm will only trigger for the specified absolute
   date/time, along with any specified repeating instances.
   If the trigger is set relative to START, then the "DTSTART" property
   MUST be present in the associated "VEVENT" or "VTODO" calendar
   component. If an alarm is specified for an event with the trigger set
   relative to the END, then the "DTEND" property or the "DSTART" and
   "DURATION' properties MUST be present in the associated "VEVENT"
   calendar component. If the alarm is specified for a to-do with a
   trigger set relative to the END, then either the "DUE" property or
   the "DSTART" and "DURATION' properties MUST be present in the
   associated "VTODO" calendar component.
   Alarms specified in an event or to-do which is defined in terms of a
   DATE value type will be triggered relative to 00:00:00 UTC on the
   specified date. For example, if "DTSTART:19980205, then the duration
   trigger will be relative to19980205T000000Z.
   Format Definition: The property is defined by the following notation:
     trigger    = "TRIGGER" (trigrel / trigabs)

     trigrel    = *(

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

                  (";" "VALUE" "=" "DURATION") /
                  (";" trigrelparam) /

                ; the following is optional,

                ; and MAY occur more than once

                  (";" xparam)
                  ) ":"  dur-value

     trigabs    = 1*(

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

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

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

                  (";" xparam)

                  ) ":" date-time

Example: A trigger set 15 minutes prior to the start of the event or to-do.
     TRIGGER:-P15M

A trigger set 5 minutes after the end of the event or to-do.
     TRIGGER;RELATED=END:P5M

A trigger set to an absolute date/time.
     TRIGGER;VALUE=DATE-TIME:19980101T050000Z

4.8.7 Change Management Component Properties

The following properties specify change management information in calendar components.


4.8.7.1 Date/Time Created

Property Name: CREATED

   Purpose: This property specifies the date and time that the calendar
   information was created by the calendar user agent in the calendar
   store.
        Note: This is analogous to the creation date and time for a file
        in the file system.

Value Type: DATE-TIME
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: The property can be specified once in "VEVENT", "VTODO"
   or "VJOURNAL" calendar components.
   Description: The date and time is a UTC value.
   Format Definition: The property is defined by the following notation:
     created    = "CREATED" creaparam ":" date-time CRLF

     creaparam  = *(";" xparam)

Example: The following is an example of this property:
     CREATED:19960329T133000Z

4.8.7.2 Date/Time Stamp

Property Name: DTSTAMP

   Purpose: The property indicates the date/time that the instance of
   the iCalendar object was created.
   Value Type: DATE-TIME
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property MUST be included in the "VEVENT", "VTODO",
   "VJOURNAL" or "VFREEBUSY" calendar components.
   Description: The value MUST be specified in the UTC time format.
   This property is also useful to protocols such as [IMIP] that have
   inherent latency issues with the delivery of content. This property
   will assist in the proper sequencing of messages containing iCalendar
   objects.
   This property is different than the "CREATED" and "LAST-MODIFIED"
   properties. These two properties are used to specify when the
   particular calendar data in the calendar store was created and last
   modified. This is different than when the iCalendar object
   representation of the calendar service information was created or
   last modified.
   Format Definition: The property is defined by the following notation:
     dtstamp    = "DTSTAMP" stmparam ":" date-time CRLF

     stmparam   = *(";" xparam)

Example:
     DTSTAMP:19971210T080000Z

4.8.7.3 Last Modified

Property Name: LAST-MODIFIED

   Purpose: The property specifies the date and time that the
   information associated with the calendar component was last revised
   in the calendar store.
        Note: This is analogous to the modification date and time for a
        file in the file system.

Value Type: DATE-TIME
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: This property can be specified in the "EVENT", "VTODO",
   "VJOURNAL" or "VTIMEZONE" calendar components.
   Description: The property value MUST be specified in the UTC time
   format.
   Format Definition: The property is defined by the following notation:
     last-mod   = "LAST-MODIFIED" lstparam ":" date-time CRLF

     lstparam   = *(";" xparam)

Example: The following is are examples of this property:
     LAST-MODIFIED:19960817T133000Z

4.8.7.4 Sequence Number

Property Name: SEQUENCE

   Purpose: This property defines the revision sequence number of the
   calendar component within a sequence of revisions.
   Value Type: integer
   Property Parameters: Non-standard property parameters can be
   specified on this property.
   Conformance: The property can be specified in "VEVENT", "VTODO" or
   "VJOURNAL" calendar component.
   Description: When a calendar component is created, its sequence
   number is zero (US-ASCII decimal 48). It is monotonically incremented
   by the "Organizer's" CUA each time the "Organizer" makes a
   significant revision to the calendar component. When the "Organizer"
   makes changes to one of the following properties, the sequence number
   MUST be incremented:
     .  "DTSTART"

     .  "DTEND"

     .  "DUE"

     .  "RDATE"

     .  "RRULE"

     .  "EXDATE"

     .  "EXRULE"

     .  "STATUS"

In addition, changes made by the "Organizer" to other properties can also force the sequence number to be incremented. The "Organizer" CUA MUST increment the sequence number when ever it makes changes to properties in the calendar component that the "Organizer" deems will jeopardize the validity of the participation status of the "Attendees". For example, changing the location of a meeting from one locale to another distant locale could effectively impact the participation status of the "Attendees".
   The "Organizer" includes this property in an iCalendar object that it
   sends to an "Attendee" to specify the current version of the calendar
   component.
   The "Attendee" includes this property in an iCalendar object that it
   sends to the "Organizer" to specify the version of the calendar
   component that the "Attendee" is referring to.
   A change to the sequence number is not the mechanism that an
   "Organizer" uses to request a response from the "Attendees". The
   "RSVP" parameter on the "ATTENDEE" property is used by the
   "Organizer" to indicate that a response from the "Attendees" is
   requested.
   Format Definition: This property is defined by the following
   notation:
     seq = "SEQUENCE" seqparam ":" integer CRLF
     ; Default is "0"

     seqparam   = *(";" xparam)

Example: The following is an example of this property for a calendar component that was just created by the "Organizer".
     SEQUENCE:0

The following is an example of this property for a calendar component that has been revised two different times by the "Organizer".
     SEQUENCE:2

4.8.8 Miscellaneous Component Properties

The following properties specify information about a number of miscellaneous features of calendar components.


4.8.8.1 Non-standard Properties

Property Name: Any property name with a "X-" prefix

   Purpose: This class of property provides a framework for defining
   non-standard properties.
   Value Type: TEXT
   Property Parameters: Non-standard and language property parameters
   can be specified on this property.
   Conformance: This property can be specified in any calendar
   component.
   Description: The MIME Calendaring and Scheduling Content Type
   provides a "standard mechanism for doing non-standard things". This
   extension support is provided for implementers to "push the envelope"
   on the existing version of the memo. Extension properties are
   specified by property and/or property parameter names that have the
   prefix text of "X-" (the two character sequence: LATIN CAPITAL LETTER
   X character followed by the HYPEN-MINUS character). It is recommended
   that vendors concatenate onto this sentinel another short prefix text
   to identify the vendor. This will facilitate readability of the
   extensions and minimize possible collision of names between different
   vendors. User agents that support this content type are expected to
   be able to parse the extension properties and property parameters but
   can ignore them.
   At present, there is no registration authority for names of extension
   properties and property parameters. The data type for this property
   is TEXT. Optionally, the data type can be any of the other valid data
   types.
   Format Definition: The property is defined by the following notation:
     x-prop     = x-name *(";" xparam) [";" languageparam] ":" text CRLF
        ; Lines longer than 75 octets should be folded

Example: The following might be the ABC vendor's extension for an audio-clip form of subject property:
     X-ABC-MMSUBJ;X-ABC-MMSUBJTYPE=wave:http://load.noise.org/mysubj.wav

4.8.8.2 Request Status

Property Name: REQUEST-STATUS

   Purpose: This property defines the status code returned for a
   scheduling request.
   Value Type: TEXT
   Property Parameters: Non-standard and language property parameters
   can be specified on this property.
   Conformance: The property can be specified in "VEVENT", "VTODO",
   "VJOURNAL" or "VFREEBUSY" calendar component.
   Description: This property is used to return status code information
   related to the processing of an associated iCalendar object. The data
   type for this property is TEXT.
   The value consists of a short return status component, a longer
   return status description component, and optionally a status-specific
   data component. The components of the value are separated by the
   SEMICOLON character (US-ASCII decimal 59).
   The short return status is a PERIOD character (US-ASCII decimal 46)
   separated 3-tuple of integers. For example, "3.1.1". The successive
   levels of integers provide for a successive level of status code
   granularity.
   The following are initial classes for the return status code.
   Individual iCalendar object methods will define specific return
   status codes for these classes. In addition, other classes for the
   return status code may be defined using the registration process
   defined later in this memo.
     |==============+===============================================|
     | Short Return | Longer Return Status Description              |
     | Status Code  |                                               |
     |==============+===============================================|
     |    1.xx      | Preliminary success. This class of status     |
     |              | of status code indicates that the request has |
     |              | request has been initially processed but that |
     |              | completion is pending.                        |
     |==============+===============================================|
     |    2.xx      | Successful. This class of status code         |
     |              | indicates that the request was completed      |
     |              | successfuly. However, the exact status code   |
     |              | can indicate that a fallback has been taken.  |
     |==============+===============================================|
     |    3.xx      | Client Error. This class of status code       |
     |              | indicates that the request was not successful.|
     |              | The error is the result of either a syntax or |
     |              | a semantic error in the client formatted      |
     |              | request. Request should not be retried until  |
     |              | the condition in the request is corrected.    |
     |==============+===============================================|
     |    4.xx      | Scheduling Error. This class of status code   |
     |              | indicates that the request was not successful.|
     |              | Some sort of error occurred within the        |
     |              | calendaring and scheduling service, not       |
     |              | directly related to the request itself.       |
     |==============+===============================================|

Format Definition: The property is defined by the following notation:
     rstatus    = "REQUEST-STATUS" rstatparam ":"
                  statcode ";" statdesc [";" extdata]

     rstatparam = *(

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

                (";" languageparm) /

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

                (";" xparam)

                )

     statcode   = 1*DIGIT *("." 1*DIGIT)
     ;Hierarchical, numeric return status code

     statdesc   = text
     ;Textual status description

     extdata    = text
     ;Textual exception data. For example, the offending property
     ;name and value or complete property line.

   Example: The following are some possible examples of this property.
   The COMMA and SEMICOLON separator characters in the property value
   are BACKSLASH character escaped because they appear in a  text value.

     REQUEST-STATUS:2.0;Success

     REQUEST-STATUS:3.1;Invalid property value;DTSTART:96-Apr-01

     REQUEST-STATUS:2.8; Success\, repeating event ignored. Scheduled
      as a single event.;RRULE:FREQ=WEEKLY\;INTERVAL=2

     REQUEST-STATUS:4.1;Event conflict. Date/time is busy.

     REQUEST-STATUS:3.7;Invalid calendar user;ATTENDEE:
      MAILTO:jsmith@host.com

5 iCalendar Object Examples

The following examples are provided as an informational source of illustrative iCalendar objects consistent with this content type.

   The following example specifies a three-day conference that begins at
   8:00 AM EDT, September 18, 1996 and end at 6:00 PM EDT, September 20,
   1996.
     BEGIN:VCALENDAR
     PRODID:-//xyz Corp//NONSGML PDA Calendar Verson 1.0//EN
     VERSION:2.0
     BEGIN:VEVENT
     DTSTAMP:19960704T120000Z
     UID:uid1@host.com
     ORGANIZER:MAILTO:jsmith@host.com
     DTSTART:19960918T143000Z
     DTEND:19960920T220000Z
     STATUS:CONFIRMED

     CATEGORIES:CONFERENCE
     SUMMARY:Networld+Interop Conference
     DESCRIPTION:Networld+Interop Conference
       and Exhibit\nAtlanta World Congress Center\n
      Atlanta, Georgia
     END:VEVENT
     END:VCALENDAR

The following example specifies a group scheduled meeting that begin at 8:30 AM EST on March 12, 1998 and end at 9:30 AM EST on March 12, 1998. The "Organizer" has scheduled the meeting with one or more calendar users in a group. A time zone specification for Eastern United States has been specified.
     BEGIN:VCALENDAR
     PRODID:-//RDU Software//NONSGML HandCal//EN
     VERSION:2.0
     BEGIN:VTIMEZONE
     TZID:US-Eastern
     BEGIN:STANDARD
     DTSTART:19981025T020000
     RDATE:19981025T020000
     TZOFFSETFROM:-0400
     TZOFFSETTO:-0500
     TZNAME:EST
     END:STANDARD
     BEGIN:DAYLIGHT
     DTSTART:19990404T020000
     RDATE:19990404T020000
     TZOFFSETFROM:-0500
     TZOFFSETTO:-0400
     TZNAME:EDT
     END:DAYLIGHT
     END:VTIMEZONE
     BEGIN:VEVENT
     DTSTAMP:19980309T231000Z
     UID:guid-1.host1.com
     ORGANIZER;ROLE=CHAIR:MAILTO:mrbig@host.com
     ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT;CUTYPE=GROUP:
      MAILTO:employee-A@host.com
     DESCRIPTION:Project XYZ Review Meeting
     CATEGORIES:MEETING
     CLASS:PUBLIC
     CREATED:19980309T130000Z
     SUMMARY:XYZ Project Review
     DTSTART;TZID=US-Eastern:19980312T083000
     DTEND;TZID=US-Eastern:19980312T093000
     LOCATION:1CP Conference Room 4350
     END:VEVENT
     END:VCALENDAR

The following is an example of an iCalendar object passed in a MIME message with a single body part consisting of a "text/calendar" Content Type.
     TO:jsmith@host1.com
     FROM:jdoe@host1.com
     MIME-VERSION:1.0
     MESSAGE-ID:<id3@host1.com>
     CONTENT-TYPE:text/calendar

     BEGIN:VCALENDAR
     METHOD:xyz
     VERSION:2.0
     PRODID:-//ABC Corporation//NONSGML My Product//EN
     BEGIN:VEVENT
     DTSTAMP:19970324T1200Z
     SEQUENCE:0
     UID:uid3@host1.com
     ORGANIZER:MAILTO:jdoe@host1.com
     ATTENDEE;RSVP=TRUE:MAILTO:jsmith@host1.com
     DTSTART:19970324T123000Z
     DTEND:19970324T210000Z
     CATEGORIES:MEETING,PROJECT
     CLASS:PUBLIC
     SUMMARY:Calendaring Interoperability Planning Meeting
     DESCRIPTION:Discuss how we can test c&s interoperability\n
      using iCalendar and other IETF standards.
     LOCATION:LDB Lobby
     ATTACH;FMTTYPE=application/postscript:ftp://xyzCorp.com/pub/
      conf/bkgrnd.ps
     END:VEVENT
     END:VCALENDAR

The following is an example of a to-do due on April 15, 1998. An audio alarm has been specified to remind the calendar user at noon, the day before the to-do is expected to be completed and repeat hourly, four additional times. The to-do definition has been modified twice since it was initially created.
     BEGIN:VCALENDAR
     VERSION:2.0
     PRODID:-//ABC Corporation//NONSGML My Product//EN
     BEGIN:VTODO
     DTSTAMP:19980130T134500Z
     SEQUENCE:2
     UID:uid4@host1.com
     ORGANIZER:MAILTO:unclesam@us.gov
     ATTENDEE;PARTSTAT=ACCEPTED:MAILTO:jqpublic@host.com

     DUE:19980415T235959
     STATUS:NEEDS-ACTION
     SUMMARY:Submit Income Taxes
     BEGIN:VALARM
     ACTION:AUDIO
     TRIGGER:19980403T120000
     ATTACH;FMTTYPE=audio/basic:http://host.com/pub/audio-
      files/ssbanner.aud
     REPEAT:4
     DURATION:PT1H
     END:VALARM
     END:VTODO
     END:VCALENDAR

The following is an example of a journal entry.
     BEGIN:VCALENDAR
     VERSION:2.0
     PRODID:-//ABC Corporation//NONSGML My Product//EN
     BEGIN:VJOURNAL
     DTSTAMP:19970324T120000Z
     UID:uid5@host1.com
     ORGANIZER:MAILTO:jsmith@host.com
     STATUS:DRAFT
     CLASS:PUBLIC
     CATEGORY:Project Report, XYZ, Weekly Meeting
     DESCRIPTION:Project xyz Review Meeting Minutes\n
      Agenda\n1. Review of project version 1.0 requirements.\n2.
     Definition
      of project processes.\n3. Review of project schedule.\n
      Participants: John Smith, Jane Doe, Jim Dandy\n-It was
       decided that the requirements need to be signed off by
       product marketing.\n-Project processes were accepted.\n
      -Project schedule needs to account for scheduled holidays
       and employee vacation time. Check with HR for specific
       dates.\n-New schedule will be distributed by Friday.\n-
      Next weeks meeting is cancelled. No meeting until 3/23.
     END:VJOURNAL
     END:VCALENDAR

The following is an example of published busy time information. The iCalendar object might be placed in the network resource www.host.com/calendar/busytime/jsmith.ifb.
     BEGIN:VCALENDAR
     VERSION:2.0
     PRODID:-//RDU Software//NONSGML HandCal//EN
     BEGIN:VFREEBUSY

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

6 Recommended Practices

These recommended practices should be followed in order to assure consistent handling of the following cases for an iCalendar object.

   1.  Content lines longer than 75 octets SHOULD be folded.

   2.  A calendar entry with a "DTSTART" property but no "DTEND"
       property does not take up any time. It is intended to represent
       an event that is associated with a given calendar date and time
       of day, such as an anniversary. Since the event does not take up
       any time, it MUST NOT be used to record busy time no matter what
       the value for the "TRANSP" property.

   3.  When the "DTSTART" and "DTEND", for "VEVENT", "VJOURNAL" and
       "VFREEBUSY" calendar components, and "DTSTART" and "DUE", for
       "VTODO" calendar components, have the same value data type (e.g.,
       DATE-TIME), they SHOULD specify values in the same time format
       (e.g., UTC time format).

   4.  When the combination of the "RRULE" and "RDATE" properties on an
       iCalendar object produces multiple instances having the same
       start date/time, they should be collapsed to, and considered as,
       a single instance.

   5.  When a calendar user receives multiple requests for the same
       calendar component (e.g., REQUEST for a "VEVENT" calendar
       component) as a result of being on multiple mailing lists
       specified by "ATTENDEE" properties in the request, they SHOULD
       respond to only one of the requests. The calendar user SHOULD
       also specify (using the "MEMBER" parameter of the "ATTENDEE"
       property) which mailing list they are a member of.

   6.  An implementation can truncate a "SUMMARY" property value to 255
       characters.

   7.  If seconds of the minute are not supported by an implementation,
       then a value of "00" SHOULD be specified for the seconds
       component in a time value.

   8.  If the value type parameter (VALUE=) contains an unknown value
       type, it SHOULD be treated as TEXT.

   9.  TZURL values SHOULD NOT be specified as a FILE URI type. This URI
       form can be useful within an organization, but is problematic in
       the Internet.

   10.  Some possible English values for CATEGORIES property include
        "ANNIVERSARY", "APPOINTMENT", "BUSINESS", "EDUCATION",
        "HOLIDAY", "MEETING", "MISCELLANEOUS", "NON-WORKING HOURS", "NOT
        IN OFFICE", "PERSONAL", "PHONE CALL", "SICK DAY", "SPECIAL
        OCCASION", "TRAVEL", "VACATION". Categories can be specified in
        any registered language.

   11.  Some possible English values for RESOURCES property include
        "CATERING", "CHAIRS", "COMPUTER PROJECTOR", "EASEL", "OVERHEAD
        PROJECTOR", "SPEAKER PHONE", "TABLE", "TV", "VCR", "VIDEO
        PHONE", "VEHICLE". Resources can be specified in any registered
        language.

7 Registration of Content Type Elements

This section provides the process for registration of MIME Calendaring and Scheduling Content Type iCalendar object methods and new or modified properties.


7.1 Registration of New and Modified iCalendar Object Methods

New MIME Calendaring and Scheduling Content Type iCalendar object methods are registered by the publication of an IETF Request for Comments (RFC). Changes to an iCalendar object method are registered by the publication of a revision of the RFC defining the method.


7.2 Registration of New Properties

This section defines procedures by which new properties or enumerated property values for the MIME Calendaring and Scheduling Content Type can be registered with the IANA. Non-IANA properties can be used by bilateral agreement, provided the associated properties names follow the "X-" convention.

   The procedures defined here are designed to allow public comment and
   review of new properties, while posing only a small impediment to the
   definition of new properties.
   Registration of a new property is accomplished by the following
   steps.

7.2.1 Define the property

A property is defined by completing the following template.

     To: ietf-calendar@imc.org

     Subject: Registration of text/calendar MIME property XXX

     Property name:

     Property purpose:

     Property value type(s):

     Property parameter (s):

     Conformance:

     Description:

     Format definition:

     Examples:

The meaning of each field in the template is as follows.
   Property name: The name of the property, as it will appear in the
   body of an text/calendar MIME Content-Type "property: value" line to
   the left of the colon ":".
   Property purpose: The purpose of the property (e.g., to indicate a
   delegate for the event or to-do, etc.). Give a short but clear
   description.
   Property value type (s): Any of the valid value types for the
   property value needs to be specified. The default value type also
   needs to be specified. If a new value type is specified, it needs to
   be declared in this section.
   Property parameter (s): Any of the valid property parameters for the
   property needs to be specified.
   Conformance: The calendar components that the property can appear in
   needs to be specified.
   Description: Any special notes about the property, how it is to be
   used, etc.
   Format definition: The ABNF for the property definition needs to be
   specified.
   Examples: One or more examples of instances of the property needs to
   be specified.

7.2.2 Post the Property definition

The property description MUST be posted to the new property discussion list, ietf-calendar@imc.org.


7.2.3 Allow a comment period

Discussion on the new property MUST be allowed to take place on the list for a minimum of two weeks. Consensus MUST be reached on the property before proceeding to the next step.


7.2.4 Submit the property for approval

Once the two-week comment period has elapsed, and the proposer is convinced consensus has been reached on the property, the registration application should be submitted to the Method Reviewer for approval. The Method Reviewer is appointed to the Application Area Directors and can either accept or reject the property registration. An accepted registration should be passed on by the Method Reviewer to the IANA for inclusion in the official IANA method registry. The registration can be rejected for any of the following reasons. 1) Insufficient comment period; 2) Consensus not reached; 3) Technical deficiencies raised on the list or elsewhere have not been addressed. The Method Reviewer's decision to reject a property can be appealed by the proposer to the IESG, or the objections raised can be addressed by the proposer and the property resubmitted.


7.3 Property Change Control

Existing properties can be changed using the same process by which they were registered.

        1.           Define the change

        2.           Post the change

        3.           Allow a comment period

        4.           Submit the property for approval

Note that the original author or any other interested party can propose a change to an existing property, but that such changes should only be proposed when there are serious omissions or errors in the published memo. The Method Reviewer can object to a change if it is not backward compatible, but is not required to do so.
   Property definitions can never be deleted from the IANA registry, but
   properties which are no longer believed to be useful can be declared
   OBSOLETE by a change to their "intended use" field.

8 References


   [IMIP]     Dawson, F., Mansour, S. and S. Silverberg, "iCalendar
              Message-based Interoperability Protocol (IMIP)", RFC 2447,
              November 1998.

   [ITIP]     Silverberg, S., Mansour, S., Dawson, F. and R. Hopson,
              "iCalendar Transport-Independent Interoperability Protocol
              (iTIP) : Scheduling Events, Busy Time, To-dos and Journal
              Entries", RFC 2446, November 1998.

   [ISO 8601] ISO 8601, "Data elements and interchange formats-
              Information interchange--Representation of dates and
              times", International Organization for Standardization,
              June, 1988.

   [ISO 9070] ISO/IEC 9070, "Information Technology_SGML Support
              Facilities--Registration Procedures for Public Text Owner
              Identifiers", Second Edition, International Organization
              for Standardization, April 1991.

   [RFC 822]  Crocker, D., "Standard for the Format of ARPA Internet
              Text Messages", STD 11, RFC 822, August 1982.

   [RFC 1738] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform
              Resource Locators (URL)", RFC 1738, December 1994.

   [RFC 1766] Alvestrand, H., "Tags for the Identification of
              Languages", RFC 1766, March 1995.

   [RFC 2045] Freed, N. and N. Borenstein, " Multipurpose Internet Mail
              Extensions (MIME) - Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC 2046] Freed, N. and N. Borenstein, " Multipurpose Internet Mail
              Extensions (MIME) - Part Two: Media Types", RFC 2046,
              November 1996.

   [RFC 2048] Freed, N., Klensin, J. and J. Postel, "Multipurpose
              Internet Mail Extensions (MIME) - Part Four: Registration
              Procedures", RFC 2048, January 1997.

   [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC 2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 2234, November 1997.

   [RFC 2279] Yergeau, F., "UTF-8, a transformation format of ISO
              10646", RFC 2279, January 1998.

   [RFC 2425] Howes, T., Smith, M. and F. Dawson, "A MIME Content-Type
              for Directory Information", RFC 2425, September 1998.

   [RFC 2426] Dawson, F. and T. Howes, "vCard MIME Directory Profile",
              RFC 2426, September 1998.

   [TZ]       Olson, A.D., et al, Time zone code and data,
              ftp://elsie.nci.nih.gov/pub/, updated periodically.

   [VCAL]     Internet Mail Consortium, "vCalendar - The Electronic
              Calendaring and Scheduling Exchange Format",
              http://www.imc.org/pdi/vcal-10.txt, September 18, 1996.

9 Acknowledgments

A hearty thanks to the IETF Calendaring and Scheduling Working Group and also the following individuals who have participated in the drafting, review and discussion of this memo:

   Roland Alden, Harald T. Alvestrand, Eric Berman, Denis Bigorgne, John
   Binici, Bill Bliss, Philippe Boucher, Steve Carter, Andre
   Courtemanche, Dave Crocker, David Curley, Alec Dun, John Evans, Ross
   Finlayson, Randell Flint, Ned Freed, Patrik Faltstrom, Chuck
   Grandgent, Mark Handley, Steve Hanna, Paul B. Hill, Paul Hoffman,
   Ross Hopson, Mark Horton, Daryl Huff, Bruce Kahn, C. Harald Koch,
   Ryan Jansen, Don Lavange, Antoine Leca, Theodore Lorek, Steve
   Mansour, Skip Montanaro, Keith Moore, Cecil Murray, Chris Newman,
   John Noerenberg, Ralph Patterson, Pete Resnick, Keith Rhodes, Robert
   Ripberger, John Rose, Doug Royer, Andras Salamar, Ted Schuh, Vinod
   Seraphin, Derrick Shadel, Ken Shan, Andrew Shuman, Steve Silverberg,
   William P. Spencer, John Sun, Mark Towfiq, Yvonne Tso, Robert Visnov,
   James L. Weiner, Mike Weston, William Wyatt.

10 Authors' and Chairs' Addresses

The following address information is provided in a MIME-VCARD, Electronic Business Card, format.

   The authors of this memo are:
   BEGIN:VCARD
   VERSION:3.0
   N:Dawson;Frank
   FN:Frank Dawson
   ORG:Lotus Development Corporation
   ADR;TYPE=WORK,POSTAL,PARCEL:;;6544 Battleford Drive;
    Raleigh;NC;27613-3502;USA
   TEL;TYPE=WORK,MSG:+1-919-676-9515
   TEL;TYPE=WORK,FAX:+1-919-676-9564
   EMAIL;TYPE=PREF,INTERNET:Frank_Dawson@Lotus.com
   EMAIL;TYPE=INTERNET:fdawson@earthlink.net
   URL:http://home.earthlink.net/~fdawson
   END:VCARD

   BEGIN:VCARD
   VERSION:3.0
   N:Stenerson;Derik
   FN:Derik Stenerson
   ORG:Microsoft Corporation
   ADR;TYPE=WORK,POSTAL,PARCEL:;;One Microsoft Way;
    Redmond;WA;98052-6399;USA
   TEL;TYPE=WORK,MSG:+1-425-936-5522
   TEL;TYPE=WORK,FAX:+1-425-936-7329
   EMAIL;TYPE=INTERNET:deriks@Microsoft.com
   END:VCARD

The iCalendar object is a result of the work of the Internet Engineering Task Force Calendaring and Scheduling Working Group. The chairmen of that working group are:
   BEGIN:VCARD
   VERSION:3.0
   N:Ganguly;Anik
   FN:Anik Ganguly
   ORG: Open Text Inc.
   ADR;TYPE=WORK,POSTAL,PARCEL:;Suite 101;38777 West Six Mile Road;
    Livonia;MI;48152;USA
   TEL;TYPE=WORK,MSG:+1-734-542-5955
   EMAIL;TYPE=INTERNET:ganguly@acm.org
   END:VCARD

The co-chairman of that working group is:
   BEGIN:VCARD
   VERSION:3.0
   N:Moskowitz;Robert
   FN:Robert Moskowitz
   EMAIL;TYPE=INTERNET:rgm-ietf@htt-consult.com
   END:VCARD

11 Full Copyright Statement

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

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.
   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.
   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.