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Network Working Group                               Frank Dawson, Lotus
Internet Draft                               Derik Stenerson, Microsoft
<draft-ietf-calsch-ical-07.txt
Expires six months after                                   May 11, 1998


     Internet Calendaring and Scheduling Core Object Specification
                              (iCalendar)


Status of this Memo

   This memo is an Internet-Draft. Internet-Drafts are working documents
   of the Internet Engineering Task Force (IETF), its areas, and its
   working groups. Note that other groups can also distribute working
   documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months. Internet-Drafts can be updated, replaced, or made obsolete by
   other documents at any time. It is not appropriate to use Internet-
   Drafts as reference material or to cite them other than as a "working
   draft" or "work in progress".

   To view the entire list of current Internet-Drafts, please check
   the "1id-abstracts.txt" listing contained in the Internet-Drafts
   Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net
   (Northern Europe), ftp.nis.garr.it (Southern Europe), munnari.oz.au
   (Pacific Rim), ftp.ietf.org (US East Coast), or ftp.isi.edu
   (US West Coast).

   Distribution of this memo is unlimited.

   Copyright (C) The Internet Society 1997. All Rights Reserved.


Abstract

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

   This memo is formatted as a registration for a MIME media type per
   [RFC 2048]. However, the format in this memo is equally applicable
   for use outside of a MIME message content type.

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

   This MIME media type provides a standard content type for capturing
   calendar event, to-do and journal entry information. It also can be
   used to convey free/busy time information. The content type is
   suitable as a MIME message entity that can be transferred over MIME
   based email systems, using HTTP or some other Internet transport. In


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   addition, the content type is useful as an object for interactions
   between desktop applications using the operating system clipboard,
   drag/drop or file systems capabilities.

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

   Readers may also refer to the calendaring and scheduling model
   defined in [ICMS] for a description of this Internet application.

   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.
































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   Table of Contents


1 Introduction.........................................................6
2 Basic Grammar and Conventions........................................6
 2.1 Formatting Conventions ...........................................7
 2.2 Related Memos ....................................................8
 2.3 International Considerations .....................................8
3 Registration Information.............................................8
 3.1 Content Type .....................................................9
 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......................................12
 4.1 Content Lines ...................................................12
  4.1.1 List and Field Separators ....................................15
  4.1.2 Multiple Values ..............................................15
  4.1.3 Binary Content ...............................................16
  4.1.4 Character Set ................................................16
 4.2 Property Parameters .............................................16
  4.2.1 Alternate Text Representation ................................17
  4.2.2 Common Name ..................................................18
  4.2.3 Calendar User Type ...........................................19
  4.2.4 Delegators ...................................................19
  4.2.5 Delegatees ...................................................20
  4.2.6 Directory Entry Reference ....................................20
  4.2.7 Inline Encoding ..............................................20
  4.2.8 Free/Busy Time Type ..........................................21
  4.2.9 Language .....................................................22
  4.2.10 Group or List Membership ....................................22
  4.2.11 Participation Status ........................................23
  4.2.12 Recurrence Identifier Range .................................24
  4.2.13 Alarm Trigger Relationship ..................................25
  4.2.14 Relationship Type ...........................................25
  4.2.15 Participation Role ..........................................26
  4.2.16 RSVP Expectation ............................................27
  4.2.17 Sent By .....................................................27
  4.2.18 Time Zone Identifier ........................................27
  4.2.19 Value Data Types ............................................28
 4.3 Property Value Data Types .......................................29
  4.3.1 Binary .......................................................29
  4.3.2 Boolean ......................................................30
  4.3.3 Calendar User Address ........................................30
  4.3.4 Date .........................................................31


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  4.3.5 Date-Time ....................................................31
  4.3.6 Duration .....................................................33
  4.3.7 Float ........................................................34
  4.3.8 Integer ......................................................34
  4.3.9 Period of Time ...............................................35
  4.3.10 Recurrence Rule .............................................36
  4.3.11 Text ........................................................40
  4.3.12 Time ........................................................41
  4.3.13 URI .........................................................43
  4.3.14 UTC Offset ..................................................44
 4.4 iCalendar Object ................................................45
 4.5 Property ........................................................45
 4.6 Calendar Components .............................................45
  4.6.1 Event Component ..............................................46
  4.6.2 To-do Component ..............................................48
  4.6.3 Journal Component ............................................49
  4.6.4 Free/Busy Component ..........................................50
  4.6.5 Time Zone Component ..........................................52
  4.6.6 Alarm Component ..............................................58
 4.7 Calendar Properties .............................................61
  4.7.1 Calendar Scale ...............................................61
  4.7.2 Method .......................................................62
  4.7.3 Product Identifier ...........................................63
  4.7.4 Version ......................................................63
 4.8 Component Properties ............................................64
  4.8.1 Descriptive Component Properties .............................64
    4.8.1.1 Attachment ...............................................64
    4.8.1.2 Categories ...............................................65
    4.8.1.3 Classification ...........................................66
    4.8.1.4 Comment ..................................................67
    4.8.1.5 Description ..............................................67
    4.8.1.6 Geographic Position ......................................68
    4.8.1.7 Location .................................................69
    4.8.1.8 Percent Complete .........................................69
    4.8.1.9 Priority .................................................70
    4.8.1.10 Resources ...............................................72
    4.8.1.11 Status ..................................................72
    4.8.1.12 Summary .................................................73
  4.8.2 Date and Time Component Properties ...........................74
    4.8.2.1 Date/Time Completed ......................................74
    4.8.2.2 Date/Time End ............................................75
    4.8.2.3 Date/Time Due ............................................75
    4.8.2.4 Date/Time Start ..........................................76
    4.8.2.5 Duration .................................................77
    4.8.2.6 Free/Busy Time ...........................................78
    4.8.2.7 Time Transparency ........................................79
  4.8.3 Time Zone Component Properties ...............................79
    4.8.3.1 Time Zone Identifier .....................................79
    4.8.3.2 Time Zone Name ...........................................80
    4.8.3.3 Time Zone Offset From ....................................81
    4.8.3.4 Time Zone Offset To ......................................82
    4.8.3.5 Time Zone URL ............................................82
  4.8.4 Relationship Component Properties ............................83
    4.8.4.1 Attendee .................................................83


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    4.8.4.2 Contact ..................................................85
    4.8.4.3 Organizer ................................................86
    4.8.4.4 Recurrence ID ............................................87
    4.8.4.5 Related To ...............................................88
    4.8.4.6 Uniform Resource Locator .................................89
    4.8.4.7 Unique Identifier ........................................90
  4.8.5 Recurrence Component Properties ..............................91
    4.8.5.1 Exception Date/Times .....................................91
    4.8.5.2 Exception Rule ...........................................92
    4.8.5.3 Recurrence Date/Times ....................................93
    4.8.5.4 Recurrence Rule ..........................................95
  4.8.6 Alarm Component Properties ..................................102
    4.8.6.1 Action ..................................................103
    4.8.6.2 Repeat Count ............................................103
    4.8.6.3 Trigger .................................................104
  4.8.7 Change Management Component Properties ......................105
    4.8.7.1 Date/Time Created .......................................105
    4.8.7.2 Date/Time Stamp .........................................106
    4.8.7.3 Last Modified ...........................................107
    4.8.7.4 Sequence Number .........................................107
  4.8.8 Miscellaneous Component Properties ..........................109
    4.8.8.1 Non-standard Properties .................................109
    4.8.8.2 Request Status ..........................................110
5 iCalendar Object Examples..........................................111
6 Recommended Practices..............................................115
7 Registration of Content Type Elements..............................116
 7.1 Registration of New and Modified iCalendar Object Methods ......116
 7.2 Registration of New Properties .................................116
  7.2.1 Define the property .........................................116
  7.2.2 Post the Property definition ................................117
  7.2.3 Allow a comment period ......................................117
  7.2.4 Submit the property for approval ............................117
 7.3 Property Change Control ........................................118
8 References.........................................................118
9 Acknowledgments....................................................120
10 Author's Address..................................................120
11 Full Copyright Statement..........................................121



















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1  Introduction

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

   The calendaring and scheduling model, defined in the [ICMS], is a
   useful reference to terms and the general framework of this Internet
   application.

   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



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   "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
   [MIME DIR] content type. While the iCalendar object is not a profile
   of the [MIME DIR] content type, it does reuse a number of the
   elements from the [MIME DIR] 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 [ICMS], core
   object (this memo) or interoperability protocol [ITIP] some
   formatting conventions have been used. Calendaring and scheduling
   roles defined by [ICMS] 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.



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   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.

   [ICMS] - specifies a common terminology and abstract model;

   [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.






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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)




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   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".



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   PROCEDURAL ALARMS - - An iCalendar object can be created that
   contains a "VEVENT" and "VTODO" calendar component with "VALARM"
   calendar components. The "VALARM" calendar component can be of type
   PROCEDURE and can have an attachment containing some sort of
   executable program. Implementations that incorporate these types of
   alarms are subject to any virus or malicious attack that might occur
   as a result of executing the attachment.

   ATTACHMENTS - - An iCalendar object can include references to Uniform
   Resource Locators that can be programmed resources.

   Implementers and users of this memo should be aware of the network
   security implications of accepting and parsing such information. In
   addition, the security considerations observed by implementations of
   electronic mail systems should be followed for this memo.

3.6 Interoperability Considerations

   This MIME content type is intended to define a common format for
   conveying calendaring and scheduling information between different
   systems. It is heavily based on the earlier [VCAL] industry
   specification.

3.7 Applications Which Use This Media Type

   This content-type is designed for widespread use by Internet
   calendaring and scheduling applications. In addition, applications in
   the workflow and document management area might find this content-
   type applicable. The [ITIP] and [IMIP] Internet protocols directly
   use this content-type also. Future work on an Internet calendar
   access protocol will utilize this content-type too.

3.8 Additional Information

   This memo defines this content-type.

3.9 Magic Numbers

   None.

3.10    File Extensions

   The file extension of "ics" is to be used to designate a file
   containing (an arbitrary set of) calendaring and scheduling
   information consistent with this MIME content type.

   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.


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   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,


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   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 [MIME DIR]. That
   is, the content information consists of one or more CRLF-separated
   content lines.

   The following notation defines the 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




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     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




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     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. Each value in
   a list of values MUST be separated by a COMMA character (US-ASCII
   decimal 44). There is no significance to the ordering 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 and property value fields. A COMMA is
   used to separate values.

     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


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   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]. Support for inline binary content SHOULD be restricted to
   those applications requirements that necessitate conveying the
   complete calendaring and scheduling information within a single
   iCalendar object. 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;ENCODING=BASE64;VALUE=BINARY:MIICajCCAdOgAwIBAgICBEUwD
      QYJKoZIhvcNAQEEBQAwdzELMAkGA1UEBhMCVVMxLDAqBgNVBAoTI05ldHNjY
      XBlIENvbW11bmljYXRpb25zIENvcnBvcmF0aW9uMRwwGgYDVQQLExNJbmZvc
        <...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



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   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
                / 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.


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   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 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:<li>Market
     Overview</li><li>Finances</li><li>Project Management</li></p>
     </html></body>

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





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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 URI parameter values MUST be specified in a quoted-
   string.

   Example:



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     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 whom the calendar user
   specified by the property has delegated participation to.

   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 URI
   parameter values MUST 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 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


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   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;ENCODING=BASE64;VALUE=BINARY:MIICajCCAdOgAwIBAgICBEUwD
      QYJKoZIhvcNAQEEBQAwdzELMAkGA1UEBhMCVVMxLDAqBgNVBAoTI05ldHNjY
      XBlIENvbW11bmljYXRpb25zIENvcnBvcmF0aW9uMRwwGgYDVQQLExNJbmZvc
        <...remainder of "BASE64" encoded binary data...>

4.2.8   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


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   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

4.2.9   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

4.2.10  Group or List Membership

   Parameter Name: MEMBER

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




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   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 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

4.2.11  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.


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                        / "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

4.2.12  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





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4.2.13  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

4.2.14  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


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   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>

   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

4.2.15  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



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4.2.16  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

4.2.17  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 URI parameter values MUST be specified in a
   quoted-string.

   Example:

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

4.2.18  Time Zone Identifier

   Parameter Name: TZID

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


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

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

     tzidprefix = "/"

   Description: The parameter MUST be specify 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. 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).

   The following are examples of this property parameter:

     DTSTART;TZID=America-New_York:19980119T020000

     DTEND;TZID=America-New_York: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.

4.2.19  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



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     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].


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     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 defind 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


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   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 can be
   specified using a COMMA character (US-ASCII decimal 44) separator
   character. 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


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   Description: If the property permits, multiple "date-time" values MAY
   be specified using a COMMA character (US-ASCII decimal 44) separator
   character. 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


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   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=America-New_York: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=America-NYC: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:

     duration   = (["+"] / "-") "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 can
   be specified using a COMMA character (US-ASCII decimal 44) separator


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   character. 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 value 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 can be
   specified using a COMMA character (US-ASCII decimal 44) separator
   character.

   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 can
   be specified using a COMMA character (US-ASCII decimal 44) separator


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   character. The valid range for "integer" is -2147483648 to
   2147483647. If the sign is not specified, then the value is assumed
   to be positive. If the property permits, multiple "integer" values
   can be specified using a COMMA character (US-ASCII decimal 44)
   separator character.

   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 "/" duration
     ; [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 can be
   specified using a COMMA character (US-ASCII decimal 44) separator
   character. There are two forms of a period of time. 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. 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:



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     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
                [(";" "UNTIL" "=" enddate) / (";" "COUNT" "=" 1*DIGIT)]
                [";" "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)
        ;Individual rule parts MUST only be specified once.
        ;Rule parts need not be specified in particular any order.

     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


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     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 can be
   specified using a COMMA character (US-ASCII decimal 44) separator
   character. 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


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   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" or 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


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   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]. The first calendar week
   of the year is the one that includes the first 4 days of the year. A
   week is defined as a seven day period, starting on the day of the
   week defined to be the week start (see WKST). 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


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   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 day 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: If the character set is UTF-8, the value type is
   defined by the following notation. This must be modified depending on
   character sets. For example, the definition of TSAFE-CHAR includes
   ESC for character sets that use ISO 2022 character set switching and



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   TSAFE-CHAR should not include NON-US-ASCII when the character set is
   US-ASCII.

     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, ";", ":", "\", ","

   Description: If the property permits, multiple "text" values can be
   specified using a COMMA character (US-ASCII decimal 44) separator
   character.

   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 need to 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\n Conference Room - 3B\nCome Prepared.

4.3.12  Time

   Value Name: TIME



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

   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 can be
   specified using a COMMA character (US-ASCII decimal 44) separator
   character. 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 is 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


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   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=America-New York: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:



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     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

   Description: The PLUS SIGN character MUST be specified for positive
   UTC offsets (i.e., ahead of UTC). The value of "-0000" is not
   allowed.

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

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

     -0500

     +0100






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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 = "BEGIN" ":" "VCALENDAR" CRLF
                  icalbody
                  "END" ":" "VCALENDAR" CRLF [icalobject]

   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 property 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 places no imposed 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=Eastern:19980714T120000 is the same as
   DtStart;TzID=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.



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

     icalbody   = calprops component

     calprops   = [calscale] [method] prodid version *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  = *attach *attendee *categories [class] *comment
                  *contact [created] [description] [dtend / duration]
                  [dtstart] *exdate *exrule [geo] [last-mod] [location]
                  [organizer] [priority] *rstatus *related *resources
                  *rdate *rrule [dtstamp] [seq] [status] [summary]
                  [transp] [uid] [url] [recurid] *x-prop




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   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:




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     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   = *attach *attendee *categories [class] *comment
                  [completed] *contact [created] [description] [dtstamp]
                  [dtstart] [due / duration] *exdate *exrule [geo]
                  [last-mod] [location] [organizer] [percent] [priority]
                  *rstatus *related *resources *rdate *rrule
                  [recurid] [seq] [status] [summary] [uid] [url]
                  *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".



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   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:VEVENT

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   = *attach *attendee *categories [class] *comment
                  *contact [created] [description] [dtstart] [dtstamp]
                  *exdate *exrule [last-mod] [organizer] [recurid]
                  *related *rdate *rrule *rstatus [seq] [status]
                  [summary] [uid] [url] *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.


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   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     = *attendee *comment [contact] [dtstart] [dtend]
                  [duration] [dtstamp] *freebusy [organizer] *rstatus
                  [uid] [url] *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


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   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 that 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; 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 "FREEBBUSY" 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


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     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 published 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

                  tzid [last-mod] [tzurl] 1*(standardc / daylightc)
                  *x-prop

                  "END" ":" "VTIMEZONE" CRLF

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

                  tzprop

                  "END" ":" "STANDARD" CRLF



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

                  tzprop

                  "END" ":" "DAYLIGHT" CRLF

     tzprop     = *comment dtstart (*rdate / *rrule)
                  *tzname tzoffsetto tzoffsetfrom *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 for the eastern
   United States starting from 1967. Each line represents a description
   or rule for a particular observance.

     Effective Observance Rule

     Date       (Date/Time)             Offset  Abbreviation

     1967-*     lastSun 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

   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.


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   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.


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   The optional "TZURL" property is url value that points to a published
   VTIMEZONE definition.

   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 the eastern United States:

     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" pr