Internet Calendaring and Scheduling Core Object Specification (iCalendar)
Network Working Group F. Dawson
Request for Comments: 2445 Lotus
Category: Standards Track D. Stenerson
Microsoft
November 1998
Internet Calendaring and Scheduling Core Object Specification
(iCalendar)
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1998). All Rights Reserved.
Abstract
There is a clear need to provide and deploy interoperable calendaring
and scheduling services for the Internet. Current group scheduling
and Personal Information Management (PIM) products are being extended
for use across the Internet, today, in proprietary ways. This memo
has been defined to provide the definition of a common format for
openly exchanging calendaring and scheduling information across the
Internet.
This memo is formatted as a registration for a MIME media type per
[RFC 2048]. However, the format in this memo is equally applicable
for use outside of a MIME message content type.
The proposed media type value is 'text/calendar'. This string would
label a media type containing calendaring and scheduling information
encoded as text characters formatted in a manner outlined below.
This MIME media type provides a standard content type for capturing
calendar event, to-do and journal entry information. It also can be
used to convey free/busy time information. The content type is
suitable as a MIME message entity that can be transferred over MIME
based email systems, using HTTP or some other Internet transport. In
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RFC 2445 iCalendar November 1998
addition, the content type is useful as an object for interactions
between desktop applications using the operating system clipboard,
drag/drop or file systems capabilities.
This memo is based on the earlier work of the vCalendar specification
for the exchange of personal calendaring and scheduling information.
In order to avoid confusion with this referenced work, this memo is
to be known as the iCalendar specification.
This memo defines the format for specifying iCalendar object methods.
An iCalendar object method is a set of usage constraints for the
iCalendar object. For example, these methods might define scheduling
messages that request an event be scheduled, reply to an event
request, send a cancellation notice for an event, modify or replace
the definition of an event, provide a counter proposal for an
original event request, delegate an event request to another
individual, request free or busy time, reply to a free or busy time
request, or provide similar scheduling messages for a to-do or
journal entry calendar component. The iCalendar Transport-indendent
Interoperability Protocol (iTIP) defined in [ITIP] is one such
scheduling protocol.
Table of Contents
1 Introduction.....................................................5
2 Basic Grammar and Conventions....................................6
2.1 Formatting Conventions .......................................7
2.2 Related Memos ................................................8
2.3 International Considerations .................................8
3 Registration Information.........................................8
3.1 Content Type .................................................8
3.2 Parameters ...................................................9
3.3 Content Header Fields .......................................10
3.4 Encoding Considerations .....................................10
3.5 Security Considerations .....................................10
3.6 Interoperability Considerations .............................11
3.7 Applications Which Use This Media Type ......................11
3.8 Additional Information ......................................11
3.9 Magic Numbers ...............................................11
3.10 File Extensions ............................................11
3.11 Contact for Further Information: ...........................12
3.12 Intended Usage .............................................12
3.13 Authors/Change Controllers .................................12
4 iCalendar Object Specification..................................13
4.1 Content Lines ...............................................13
4.1.1 List and Field Separators ................................16
4.1.2 Multiple Values ..........................................16
4.1.3 Binary Content ...........................................16
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4.1.4 Character Set ............................................17
4.2 Property Parameters .........................................17
4.2.1 Alternate Text Representation ............................18
4.2.2 Common Name ..............................................19
4.2.3 Calendar User Type .......................................20
4.2.4 Delegators ...............................................20
4.2.5 Delegatees ...............................................21
4.2.6 Directory Entry Reference ................................21
4.2.7 Inline Encoding ..........................................22
4.2.8 Format Type ..............................................23
4.2.9 Free/Busy Time Type ......................................23
4.2.10 Language ................................................24
4.2.11 Group or List Membership ................................25
4.2.12 Participation Status ....................................25
4.2.13 Recurrence Identifier Range .............................27
4.2.14 Alarm Trigger Relationship ..............................27
4.2.15 Relationship Type .......................................28
4.2.16 Participation Role ......................................29
4.2.17 RSVP Expectation ........................................29
4.2.18 Sent By .................................................30
4.2.19 Time Zone Identifier ....................................30
4.2.20 Value Data Types ........................................32
4.3 Property Value Data Types ...................................32
4.3.1 Binary ...................................................33
4.3.2 Boolean ..................................................33
4.3.3 Calendar User Address ....................................34
4.3.4 Date .....................................................34
4.3.5 Date-Time ................................................35
4.3.6 Duration .................................................37
4.3.7 Float ....................................................38
4.3.8 Integer ..................................................38
4.3.9 Period of Time ...........................................39
4.3.10 Recurrence Rule .........................................40
4.3.11 Text ....................................................45
4.3.12 Time ....................................................47
4.3.13 URI .....................................................49
4.3.14 UTC Offset ..............................................49
4.4 iCalendar Object ............................................50
4.5 Property ....................................................51
4.6 Calendar Components .........................................51
4.6.1 Event Component ..........................................52
4.6.2 To-do Component ..........................................55
4.6.3 Journal Component ........................................56
4.6.4 Free/Busy Component ......................................58
4.6.5 Time Zone Component ......................................60
4.6.6 Alarm Component ..........................................67
4.7 Calendar Properties .........................................73
4.7.1 Calendar Scale ...........................................73
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4.7.2 Method ...................................................74
4.7.3 Product Identifier .......................................75
4.7.4 Version ..................................................76
4.8 Component Properties ........................................77
4.8.1 Descriptive Component Properties .........................77
4.8.1.1 Attachment ...........................................77
4.8.1.2 Categories ...........................................78
4.8.1.3 Classification .......................................79
4.8.1.4 Comment ..............................................80
4.8.1.5 Description ..........................................81
4.8.1.6 Geographic Position ..................................82
4.8.1.7 Location .............................................84
4.8.1.8 Percent Complete .....................................85
4.8.1.9 Priority .............................................85
4.8.1.10 Resources ...........................................87
4.8.1.11 Status ..............................................88
4.8.1.12 Summary .............................................89
4.8.2 Date and Time Component Properties .......................90
4.8.2.1 Date/Time Completed ..................................90
4.8.2.2 Date/Time End ........................................91
4.8.2.3 Date/Time Due ........................................92
4.8.2.4 Date/Time Start ......................................93
4.8.2.5 Duration .............................................94
4.8.2.6 Free/Busy Time .......................................95
4.8.2.7 Time Transparency ....................................96
4.8.3 Time Zone Component Properties ...........................97
4.8.3.1 Time Zone Identifier .................................97
4.8.3.2 Time Zone Name .......................................98
4.8.3.3 Time Zone Offset From ................................99
4.8.3.4 Time Zone Offset To .................................100
4.8.3.5 Time Zone URL .......................................101
4.8.4 Relationship Component Properties .......................102
4.8.4.1 Attendee ............................................102
4.8.4.2 Contact .............................................104
4.8.4.3 Organizer ...........................................106
4.8.4.4 Recurrence ID .......................................107
4.8.4.5 Related To ..........................................109
4.8.4.6 Uniform Resource Locator ............................110
4.8.4.7 Unique Identifier ...................................111
4.8.5 Recurrence Component Properties .........................112
4.8.5.1 Exception Date/Times ................................112
4.8.5.2 Exception Rule ......................................114
4.8.5.3 Recurrence Date/Times ...............................115
4.8.5.4 Recurrence Rule .....................................117
4.8.6 Alarm Component Properties ..............................126
4.8.6.1 Action ..............................................126
4.8.6.2 Repeat Count ........................................126
4.8.6.3 Trigger .............................................127
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4.8.7 Change Management Component Properties ..................129
4.8.7.1 Date/Time Created ...................................129
4.8.7.2 Date/Time Stamp .....................................130
4.8.7.3 Last Modified .......................................131
4.8.7.4 Sequence Number .....................................131
4.8.8 Miscellaneous Component Properties ......................133
4.8.8.1 Non-standard Properties .............................133
4.8.8.2 Request Status ......................................134
5 iCalendar Object Examples......................................136
6 Recommended Practices..........................................140
7 Registration of Content Type Elements..........................141
7.1 Registration of New and Modified iCalendar Object Methods ..141
7.2 Registration of New Properties .............................141
7.2.1 Define the property .....................................142
7.2.2 Post the Property definition ............................143
7.2.3 Allow a comment period ..................................143
7.2.4 Submit the property for approval ........................143
7.3 Property Change Control ....................................143
8 References.....................................................144
9 Acknowledgments................................................145
10 Authors' and Chairs' Addresses................................146
11 Full Copyright Statement......................................148
1 Introduction
The use of calendaring and scheduling has grown considerably in the
last decade. Enterprise and inter-enterprise business has become
dependent on rapid scheduling of events and actions using this
information technology. However, the longer term growth of
calendaring and scheduling, is currently limited by the lack of
Internet standards for the message content types that are central to
these knowledgeware applications. This memo is intended to progress
the level of interoperability possible between dissimilar calendaring
and scheduling applications. This memo defines a MIME content type
for exchanging electronic calendaring and scheduling information. The
Internet Calendaring and Scheduling Core Object Specification, or
iCalendar, allows for the capture and exchange of information
normally stored within a calendaring and scheduling application; such
as a Personal Information Manager (PIM) or a Group Scheduling
product.
The iCalendar format is suitable as an exchange format between
applications or systems. The format is defined in terms of a MIME
content type. This will enable the object to be exchanged using
several transports, including but not limited to SMTP, HTTP, a file
system, desktop interactive protocols such as the use of a memory-
based clipboard or drag/drop interactions, point-to-point
asynchronous communication, wired-network transport, or some form of
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unwired transport such as infrared might also be used.
The memo also provides for the definition of iCalendar object methods
that will map this content type to a set of messages for supporting
calendaring and scheduling operations such as requesting, replying
to, modifying, and canceling meetings or appointments, to-dos and
journal entries. The iCalendar object methods can be used to define
other calendaring and scheduling operations such a requesting for and
replying with free/busy time data. Such a scheduling protocol is
defined in the iCalendar Transport-independent Interoperability
Protocol (iTIP) defined in [ITIP].
The memo also includes a formal grammar for the content type based on
the Internet ABNF defined in [RFC 2234]. This ABNF is required for
the implementation of parsers and to serve as the definitive
reference when ambiguities or questions arise in interpreting the
descriptive prose definition of the memo.
2 Basic Grammar and Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY" and
"OPTIONAL" in this document are to be interoperated as described in
[RFC 2119].
This memo makes use of both a descriptive prose and a more formal
notation for defining the calendaring and scheduling format.
The notation used in this memo is the ABNF notation of [RFC 2234].
Readers intending on implementing this format defined in this memo
should be familiar with this notation in order to properly interpret
the specifications of this memo.
All numeric and hexadecimal values used in this memo are given in
decimal notation.
All names of properties, property parameters, enumerated property
values and property parameter values are case-insensitive. However,
all other property values are case-sensitive, unless otherwise
stated.
Note: All indented editorial notes, such as this one, are
intended to provide the reader with additional information. The
information is not essential to the building of an
implementation conformant with this memo. The information is
provided to highlight a particular feature or characteristic of
the memo.
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The format for the iCalendar object is based on the syntax of the
[RFC 2425] content type. While the iCalendar object is not a profile
of the [RFC 2425] content type, it does reuse a number of the
elements from the [RFC 2425] specification.
2.1 Formatting Conventions
The mechanisms defined in this memo are defined in prose. Many of the
terms used to describe these have common usage that is different than
the standards usage of this memo. In order to reference within this
memo elements of the calendaring and scheduling model, core object
(this memo) or interoperability protocol [ITIP] some formatting
conventions have been used. Calendaring and scheduling roles are
referred to in quoted-strings of text with the first character of
each word in upper case. For example, "Organizer" refers to a role of
a "Calendar User" within the scheduling protocol defined by [ITIP].
Calendar components defined by this memo are referred to with
capitalized, quoted-strings of text. All calendar components start
with the letter "V". For example, "VEVENT" refers to the event
calendar component, "VTODO" refers to the to-do calendar component
and "VJOURNAL" refers to the daily journal calendar component.
Scheduling methods defined by [ITIP] are referred to with
capitalized, quoted-strings of text. For example, "REQUEST" refers to
the method for requesting a scheduling calendar component be created
or modified, "REPLY" refers to the method a recipient of a request
uses to update their status with the "Organizer" of the calendar
component.
The properties defined by this memo are referred to with capitalized,
quoted-strings of text, followed by the word "property". For example,
"ATTENDEE" property refers to the iCalendar property used to convey
the calendar address of a calendar user. Property parameters defined
by this memo are referred to with lowercase, quoted-strings of text,
followed by the word "parameter". For example, "value" parameter
refers to the iCalendar property parameter used to override the
default data type for a property value. Enumerated values defined by
this memo are referred to with capitalized text, either alone or
followed by the word "value". For example, the "MINUTELY" value can
be used with the "FREQ" component of the "RECUR" data type to specify
repeating components based on an interval of one minute or more.
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2.2 Related Memos
Implementers will need to be familiar with several other memos that,
along with this memo, form a framework for Internet calendaring and
scheduling standards. This memo, [ICAL], specifies a core
specification of objects, data types, properties and property
parameters.
[ITIP] - specifies an interoperability protocol for scheduling
between different implementations;
[IMIP] specifies an Internet email binding for [ITIP].
This memo does not attempt to repeat the specification of concepts or
definitions from these other memos. Where possible, references are
made to the memo that provides for the specification of these
concepts or definitions.
2.3 International Considerations
In the rest of this document, descriptions of characters are of the
form "character name (codepoint)", where "codepoint" is from the US-
ASCII character set. The "character name" is the authoritative
description; (codepoint) is a reference to that character in US-ASCII
or US-ASCII compatible sets (for example the ISO-8859-x family, UTF-
8, ISO-2022-xx, KOI8-R). If a non-US-ASCII compatible character set
is used, appropriate code-point from that character set MUST be
chosen instead. Use of non-US-ASCII-compatible character sets is NOT
recommended.
3 Registration Information
The Calendaring and Scheduling Core Object Specification is intended
for use as a MIME content type. However, the implementation of the
memo is in no way limited solely as a MIME content type.
3.1 Content Type
The following text is intended to register this memo as the MIME
content type "text/calendar".
To: ietf-types@uninett.no
Subject: Registration of MIME content type text/calendar.
MIME media type name: text
MIME subtype name: calendar
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3.2 Parameters
Required parameters: none
Optional parameters: charset, method, component and optinfo
The "charset" parameter is defined in [RFC 2046] for other body
parts. It is used to identify the default character set used within
the body part.
The "method" parameter is used to convey the iCalendar object method
or transaction semantics for the calendaring and scheduling
information. It also is an identifier for the restricted set of
properties and values that the iCalendar object consists of. The
parameter is to be used as a guide for applications interpreting the
information contained within the body part. It SHOULD NOT be used to
exclude or require particular pieces of information unless the
identified method definition specifically calls for this behavior.
Unless specifically forbidden by a particular method definition, a
text/calendar content type can contain any set of properties
permitted by the Calendaring and Scheduling Core Object
Specification. The "method" parameter MUST be the same value as that
specified in the "METHOD" component property in the iCalendar object.
If one is present, the other MUST also be present.
The value for the "method" parameter is defined as follows:
method = 1*(ALPHA / DIGIT / "-")
; IANA registered iCalendar object method
The "component" parameter conveys the type of iCalendar calendar
component within the body part. If the iCalendar object contains more
than one calendar component type, then multiple component parameters
MUST be specified.
The value for the "component" parameter is defined as follows:
component = ("VEVENT" / "VTODO" / "VJOURNAL" / "VFREEBUSY"
/ "VTIMEZONE" / x-name / iana-token)
The "optinfo" parameter conveys optional information about the
iCalendar object within the body part. This parameter can only
specify semantics already specified by the iCalendar object and that
can be otherwise determined by parsing the body part. In addition,
the optional information specified by this parameter MUST be
consistent with that information specified by the iCalendar object.
For example, it can be used to convey the "Attendee" response status
to a meeting request. The parameter value consists of a string value.
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RFC 2445 iCalendar November 1998
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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RFC 2445 iCalendar November 1998
PROCEDURAL ALARMS - - An iCalendar object can be created that
contains a "VEVENT" and "VTODO" calendar component with "VALARM"
calendar components. The "VALARM" calendar component can be of type
PROCEDURE and can have an attachment containing some sort of
executable program. Implementations that incorporate these types of
alarms are subject to any virus or malicious attack that might occur
as a result of executing the attachment.
ATTACHMENTS - - An iCalendar object can include references to Uniform
Resource Locators that can be programmed resources.
Implementers and users of this memo should be aware of the network
security implications of accepting and parsing such information. In
addition, the security considerations observed by implementations of
electronic mail systems should be followed for this memo.
3.6 Interoperability Considerations
This MIME content type is intended to define a common format for
conveying calendaring and scheduling information between different
systems. It is heavily based on the earlier [VCAL] industry
specification.
3.7 Applications Which Use This Media Type
This content-type is designed for widespread use by Internet
calendaring and scheduling applications. In addition, applications in
the workflow and document management area might find this content-
type applicable. The [ITIP] and [IMIP] Internet protocols directly
use this content-type also. Future work on an Internet calendar
access protocol will utilize this content-type too.
3.8 Additional Information
This memo defines this content-type.
3.9 Magic Numbers
None.
3.10 File Extensions
The file extension of "ics" is to be used to designate a file
containing (an arbitrary set of) calendaring and scheduling
information consistent with this MIME content type.
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The file extension of "ifb" is to be used to designate a file
containing free or busy time information consistent with this MIME
content type.
Macintosh file type codes: The file type code of "iCal" is to be used
in Apple MacIntosh operating system environments to designate a file
containing calendaring and scheduling information consistent with
this MIME media type.
The file type code of "iFBf" is to be used in Apple MacIntosh
operating system environments to designate a file containing free or
busy time information consistent with this MIME media type.
3.11 Contact for Further Information:
Frank Dawson
6544 Battleford Drive
Raleigh, NC 27613-3502
919-676-9515 (Telephone)
919-676-9564 (Data/Facsimile)
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)
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4 iCalendar Object Specification
The following sections define the details of a Calendaring and
Scheduling Core Object Specification. This information is intended to
be an integral part of the MIME content type registration. In
addition, this information can be used independent of such content
registration. In particular, this memo has direct applicability for
use as a calendaring and scheduling exchange format in file-, memory-
or network-based transport mechanisms.
4.1 Content Lines
The iCalendar object is organized into individual lines of text,
called content lines. Content lines are delimited by a line break,
which is a CRLF sequence (US-ASCII decimal 13, followed by US-ASCII
decimal 10).
Lines of text SHOULD NOT be longer than 75 octets, excluding the line
break. Long content lines SHOULD be split into a multiple line
representations using a line "folding" technique. That is, a long
line can be split between any two characters by inserting a CRLF
immediately followed by a single linear white space character (i.e.,
SPACE, US-ASCII decimal 32 or HTAB, US-ASCII decimal 9). Any sequence
of CRLF followed immediately by a single linear white space character
is ignored (i.e., removed) when processing the content type.
For example the line:
DESCRIPTION:This is a long description that exists on a long line.
Can be represented as:
DESCRIPTION:This is a lo
ng description
that exists on a long line.
The process of moving from this folded multiple line representation
to its single line representation is called "unfolding". Unfolding is
accomplished by removing the CRLF character and the linear white
space character that immediately follows.
When parsing a content line, folded lines MUST first be unfolded
according to the unfolding procedure described above. When generating
a content line, lines longer than 75 octets SHOULD be folded
according to the folding procedure described above.
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The content information associated with an iCalendar object is
formatted using a syntax similar to that defined by [RFC 2425]. That
is, the content information consists of CRLF-separated content lines.
The following notation defines the lines of content in an iCalendar
object:
contentline = name *(";" param ) ":" value CRLF
; This ABNF is just a general definition for an initial parsing
; of the content line into its property name, parameter list,
; and value string
; When parsing a content line, folded lines MUST first
; be unfolded according to the unfolding procedure
; described above. When generating a content line, lines
; longer than 75 octets SHOULD be folded according to
; the folding procedure described above.
name = x-name / iana-token
iana-token = 1*(ALPHA / DIGIT / "-")
; iCalendar identifier registered with IANA
x-name = "X-" [vendorid "-"] 1*(ALPHA / DIGIT / "-")
; Reservered for experimental use. Not intended for use in
; released products.
vendorid = 3*(ALPHA / DIGIT) ;Vendor identification
param = param-name "=" param-value
*("," param-value)
; Each property defines the specific ABNF for the parameters
; allowed on the property. Refer to specific properties for
; precise parameter ABNF.
param-name = iana-token / x-token
param-value = paramtext / quoted-string
paramtext = *SAFE-CHAR
value = *VALUE-CHAR
quoted-string = DQUOTE *QSAFE-CHAR DQUOTE
NON-US-ASCII = %x80-F8
; Use restricted by charset parameter
; on outer MIME object (UTF-8 preferred)
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RFC 2445 iCalendar November 1998
QSAFE-CHAR = WSP / %x21 / %x23-7E / NON-US-ASCII
; Any character except CTLs and DQUOTE
SAFE-CHAR = WSP / %x21 / %x23-2B / %x2D-39 / %x3C-7E
/ NON-US-ASCII
; Any character except CTLs, DQUOTE, ";", ":", ","
VALUE-CHAR = WSP / %x21-7E / NON-US-ASCII
; Any textual character
CR = %x0D
; carriage return
LF = %x0A
; line feed
CRLF = CR LF
; Internet standard newline
CTL = %x00-08 / %x0A-1F / %x7F
; Controls
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
DIGIT = %x30-39
; 0-9
DQUOTE = %x22
; Quotation Mark
WSP = SPACE / HTAB
SPACE = %x20
HTAB = %x09
The property value component of a content line has a format that is
property specific. Refer to the section describing each property for
a definition of this format.
All names of properties, property parameters, enumerated property
values and property parameter values are case-insensitive. However,
all other property values are case-sensitive, unless otherwise
stated.
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4.1.1 List and Field Separators
Some properties and parameters allow a list of values. Values in a
list of values MUST be separated by a COMMA character (US-ASCII
decimal 44). There is no significance to the order of values in a
list. For those parameter values (such as those that specify URI
values) that are specified in quoted-strings, the individual quoted-
strings are separated by a COMMA character (US-ASCII decimal 44).
Some property values are defined in terms of multiple parts. These
structured property values MUST have their value parts separated by a
SEMICOLON character (US-ASCII decimal 59).
Some properties allow a list of parameters. Each property parameter
in a list of property parameters MUST be separated by a SEMICOLON
character (US-ASCII decimal 59).
Property parameters with values containing a COLON, a SEMICOLON or a
COMMA character MUST be placed in quoted text.
For example, in the following properties a SEMICOLON is used to
separate property parameters from each other, and a COMMA is used to
separate property values in a value list.
ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT:MAILTO:
jsmith@host.com
RDATE;VALUE=DATE:19970304,19970504,19970704,19970904
4.1.2 Multiple Values
Some properties defined in the iCalendar object can have multiple
values. The general rule for encoding multi-valued items is to simply
create a new content line for each value, including the property
name. However, it should be noted that some properties support
encoding multiple values in a single property by separating the
values with a COMMA character (US-ASCII decimal 44). Individual
property definitions should be consulted for determining whether a
specific property allows multiple values and in which of these two
forms.
4.1.3 Binary Content
Binary content information in an iCalendar object SHOULD be
referenced using a URI within a property value. That is the binary
content information SHOULD be placed in an external MIME entity that
can be referenced by a URI from within the iCalendar object. In
applications where this is not feasible, binary content information
Dawson & Stenerson Standards Track [Page 16]
RFC 2445 iCalendar November 1998
can be included within an iCalendar object, but only after first
encoding it into text using the "BASE64" encoding method defined in
[RFC 2045]. Inline binary contact SHOULD only be used in applications
whose special circumstances demand that an iCalendar object be
expressed as a single entity. A property containing inline binary
content information MUST specify the "ENCODING" property parameter.
Binary content information placed external to the iCalendar object
MUST be referenced by a uniform resource identifier (URI).
The following example specifies an "ATTACH" property that references
an attachment external to the iCalendar object with a URI reference:
ATTACH:http://xyz.com/public/quarterly-report.doc
The following example specifies an "ATTACH" property with inline
binary encoded content information:
ATTACH;FMTTYPE=image/basic;ENCODING=BASE64;VALUE=BINARY:
MIICajCCAdOgAwIBAgICBEUwDQYJKoZIhvcNAQEEBQAwdzELMAkGA1U
EBhMCVVMxLDAqBgNVBAoTI05ldHNjYXBlIENvbW11bmljYXRpb25zIE
<...remainder of "BASE64" encoded binary data...>
4.1.4 Character Set
There is not a property parameter to declare the character set used
in a property value. The default character set for an iCalendar
object is UTF-8 as defined in [RFC 2279].
The "charset" Content-Type parameter can be used in MIME transports
to specify any other IANA registered character set.
4.2 Property Parameters
A property can have attributes associated with it. These "property
parameters" contain meta-information about the property or the
property value. Property parameters are provided to specify such
information as the location of an alternate text representation for a
property value, the language of a text property value, the data type
of the property value and other attributes.
Property parameter values that contain the COLON (US-ASCII decimal
58), SEMICOLON (US-ASCII decimal 59) or COMMA (US-ASCII decimal 44)
character separators MUST be specified as quoted-string text values.
Property parameter values MUST NOT contain the DOUBLE-QUOTE (US-ASCII
decimal 22) character. The DOUBLE-QUOTE (US-ASCII decimal 22)
character is used as a delimiter for parameter values that contain
restricted characters or URI text. For example:
Dawson & Stenerson Standards Track [Page 17]
RFC 2445 iCalendar November 1998
DESCRIPTION;ALTREP="http://www.wiz.org":The Fall'98 Wild Wizards
Conference - - Las Vegas, NV, USA
Property parameter values that are not in quoted strings are case
insensitive.
The general property parameters defined by this memo are defined by
the following notation:
parameter = altrepparam ; Alternate text representation
/ cnparam ; Common name
/ cutypeparam ; Calendar user type
/ delfromparam ; Delegator
/ deltoparam ; Delegatee
/ dirparam ; Directory entry
/ encodingparam ; Inline encoding
/ fmttypeparam ; Format type
/ fbtypeparam ; Free/busy time type
/ languageparam ; Language for text
/ memberparam ; Group or list membership
/ partstatparam ; Participation status
/ rangeparam ; Recurrence identifier range
/ trigrelparam ; Alarm trigger relationship
/ reltypeparam ; Relationship type
/ roleparam ; Participation role
/ rsvpparam ; RSVP expectation
/ sentbyparam ; Sent by
/ tzidparam ; Reference to time zone object
/ valuetypeparam ; Property value data type
/ ianaparam
; Some other IANA registered iCalendar parameter.
/ xparam
; A non-standard, experimental parameter.
ianaparam = iana-token "=" param-value *("," param-value)
xparam =x-name "=" param-value *("," param-value)
4.2.1 Alternate Text Representation
Parameter Name: ALTREP
Purpose: To specify an alternate text representation for the property
value.
Format Definition: The property parameter is defined by the following
notation:
Dawson & Stenerson Standards Track [Page 18]
RFC 2445 iCalendar November 1998
altrepparam = "ALTREP" "=" DQUOTE uri DQUOTE
Description: The parameter specifies a URI that points to an
alternate representation for a textual property value. A property
specifying this parameter MUST also include a value that reflects the
default representation of the text value. The individual URI
parameter values MUST each be specified in a quoted-string.
Example:
DESCRIPTION;ALTREP="CID:":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:
Project XYZ Review Meeting will include the following
agenda items:
- Market Overview
- Finances
- Project Management
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. Dawson & Stenerson Standards Track [Page 19]
RFC 2445 iCalendar November 1998 Example: ORGANIZER;CN="John
Smith":MAILTO:jsmith@host.com 4.2.3 Calendar User Type Parameter
Name: CUTYPE Purpose: To specify the type of calendar user
specified by the property. Format Definition: The property
parameter is defined by the following notation: cutypeparam =
"CUTYPE" "=" ("INDIVIDUAL" ; An individual / "GROUP" ; A group of
individuals / "RESOURCE" ; A physical resource / "ROOM" ; A room
resource / "UNKNOWN" ; Otherwise not known / x-name ; Experimental
type / iana-token) ; Other IANA registered ; type ; Default is
INDIVIDUAL Description: This parameter can be specified on
properties with a CAL-ADDRESS value type. The parameter identifies
the type of calendar user specified by the property. If not
specified on a property that allows this parameter, the default is
INDIVIDUAL. Example:
ATTENDEE;CUTYPE=GROUP:MAILTO:ietf-calsch@imc.org 4.2.4 Delegators
Parameter Name: DELEGATED-FROM Purpose: To specify the calendar
users that have delegated their participation to the calendar user
specified by the property. Format Definition: The property
parameter is defined by the following notation: delfromparam =
"DELEGATED-FROM" "=" DQUOTE cal-address DQUOTE *("," DQUOTE
cal-address DQUOTE) Dawson & Stenerson Standards Track [Page
20]
RFC 2445 iCalendar November 1998 Description: This parameter
can be specified on properties with a CAL-ADDRESS value type. This
parameter can be specified on a property that has a value type of
calendar address. This parameter specifies those calendar uses that
have delegated their participation in a group scheduled event or
to-do to the calendar user specified by the property. The value
MUST be a MAILTO URI as defined in [
RFC 1738]. The individual
calendar address parameter values MUST each be specified in a
quoted-string. Example:
ATTENDEE;DELEGATED-FROM="MAILTO:jsmith@host.com":MAILTO:
jdoe@host.com 4.2.5 Delegatees Parameter Name: DELEGATED-TO
Purpose: To specify the calendar users to whom the calendar user
specified by the property has delegated participation. Format
Definition: The property parameter is defined by the following
notation: deltoparam = "DELEGATED-TO" "=" DQUOTE cal-address DQUOTE
*("," DQUOTE cal-address DQUOTE) Description: This parameter can be
specified on properties with a CAL-ADDRESS value type. This
parameter specifies those calendar users whom have been delegated
participation in a group scheduled event or to-do by the calendar
user specified by the property. The value MUST be a MAILTO URI as
defined in [
RFC 1738]. The individual calendar address parameter
values MUST each be specified in a quoted-string. Example:
ATTENDEE;DELEGATED-TO="MAILTO:jdoe@host.com","MAILTO:jqpublic@
host.com":MAILTO:jsmith@host.com 4.2.6 Directory Entry Reference
Parameter Name: DIR Purpose: To specify reference to a directory
entry associated with the calendar user specified by the property.
Format Definition: The property parameter is defined by the
following notation: Dawson & Stenerson Standards Track [Page
21]
RFC 2445 iCalendar November 1998 dirparam = "DIR" "=" DQUOTE
uri DQUOTE Description: This parameter can be specified on
properties with a CAL-ADDRESS value type. The parameter specifies a
reference to the directory entry associated with the calendar user
specified by the property. The parameter value is a URI. The
individual URI parameter values MUST each be specified in a
quoted-string. Example:
ORGANIZER;DIR="ldap://host.com:6666/o=eDABC%20Industries,c=3DUS??
(cn=3DBJim%20Dolittle)":MAILTO:jimdo@host1.com 4.2.7 Inline
Encoding Parameter Name: ENCODING Purpose: To specify an alternate
inline encoding for the property value. Format Definition: The
property parameter is defined by the following notation:
encodingparam = "ENCODING" "=" ("8BIT" ; "8bit" text encoding is
defined in [
RFC 2045] / "BASE64" ; "BASE64" binary encoding format
is defined in [
RFC 2045] / iana-token ; Some other IANA registered
iCalendar encoding type / x-name) ; A non-standard, experimental
encoding type Description: The property parameter identifies the
inline encoding used in a property value. The default encoding is
"8BIT", corresponding to a property value consisting of text. The
"BASE64" encoding type corresponds to a property value encoded
using the "BASE64" encoding defined in [
RFC 2045]. If the value
type parameter is ";VALUE=BINARY", then the inline encoding
parameter MUST be specified with the value ";ENCODING=BASE64".
Dawson & Stenerson Standards Track [Page 22]
RFC 2445 iCalendar
November 1998 Example:
ATTACH;FMTYPE=IMAGE/JPEG;ENCODING=BASE64;VALUE=BINARY:MIICajC
CAdOgAwIBAgICBEUwDQYJKoZIhvcNAQEEBQAwdzELMAkGA1UEBhMCVVMxLDA
qBgNVBAoTI05ldHNjYXBlIENvbW11bmljYXRpb25zIENvcnBvcmF0aW9uMRw
<...remainder of "BASE64" encoded binary data...> 4.2.8
Format Type Parameter Name: FMTTYPE Purpose: To specify the content
type of a referenced object. Format Definition: The property
parameter is defined by the following notation: fmttypeparam =
"FMTTYPE" "=" iana-token ; A IANA registered content type / x-name
; A non-standard content type Description: This parameter can be
specified on properties that are used to reference an object. The
parameter specifies the content type of the referenced object. For
example, on the "ATTACH" property, a FTP type URI value does not,
by itself, necessarily convey the type of content associated with
the resource. The parameter value MUST be the TEXT for either an
IANA registered content type or a non-standard content type.
Example:
ATTACH;FMTTYPE=application/binary:ftp://domain.com/pub/docs/
agenda.doc 4.2.9 Free/Busy Time Type Parameter Name: FBTYPE
Purpose: To specify the free or busy time type. Format Definition:
The property parameter is defined by the following notation:
fbtypeparam = "FBTYPE" "=" ("FREE" / "BUSY" / "BUSY-UNAVAILABLE" /
"BUSY-TENTATIVE" / x-name ; Some experimental iCalendar data type.
/ iana-token) Dawson & Stenerson Standards Track [Page 23]
RFC 2445 iCalendar November 1998 ; Some other IANA registered iCalendar
data type. Description: The parameter specifies the free or busy
time type. The value FREE indicates that the time interval is free
for scheduling. The value BUSY indicates that the time interval is
busy because one or more events have been scheduled for that
interval. The value BUSY-UNAVAILABLE indicates that the time
interval is busy and that the interval can not be scheduled. The
value BUSY-TENTATIVE indicates that the time interval is busy
because one or more events have been tentatively scheduled for that
interval. If not specified on a property that allows this
parameter, the default is BUSY. Example: The following is an
example of this parameter on a FREEBUSY property.
FREEBUSY;FBTYPE=BUSY:19980415T133000Z/19980415T170000Z 4.2.10
Language Parameter Name: LANGUAGE Purpose: To specify the language
for text values in a property or property parameter. Format
Definition: The property parameter is defined by the following
notation: languageparam = "LANGUAGE" "=" language language =
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 Dawson
& Stenerson Standards Track [Page 24]
RFC 2445 iCalendar
November 1998 The following example makes use of the
Quoted-Printable encoding in order to represent non-ASCII
characters. LOCATION;LANGUAGE=da:K=F8benhavn
LOCATION;LANGUAGE=en:Copenhagen 4.2.11 Group or List Membership
Parameter Name: MEMBER Purpose: To specify the group or list
membership of the calendar user specified by the property. Format
Definition: The property parameter is defined by the following
notation: memberparam = "MEMBER" "=" DQUOTE cal-address DQUOTE
*("," DQUOTE cal-address DQUOTE) Description: This parameter can be
specified on properties with a CAL-ADDRESS value type. The
parameter identifies the groups or list membership for the calendar
user specified by the property. The parameter value either a single
calendar address in a quoted-string or a COMMA character (US-ASCII
decimal 44) list of calendar addresses, each in a quoted-string.
The individual calendar address parameter values MUST each be
specified in a quoted-string. Example:
ATTENDEE;MEMBER="MAILTO:ietf-calsch@imc.org":MAILTO:jsmith@host.com
ATTENDEE;MEMBER="MAILTO:projectA@host.com","MAILTO:projectB@host.
com":MAILTO:janedoe@host.com 4.2.12 Participation Status Parameter
Name: PARTSTAT Purpose: To specify the participation status for the
calendar user specified by the property. Format Definition: The
property parameter is defined by the following notation:
partstatparam = "PARTSTAT" "=" ("NEEDS-ACTION" ; Event needs action
/ "ACCEPTED" ; Event accepted / "DECLINED" ; Event declined Dawson
& Stenerson Standards Track [Page 25]
RFC 2445 iCalendar
November 1998 / "TENTATIVE" ; Event tentatively ; accepted /
"DELEGATED" ; Event delegated / x-name ; Experimental status /
iana-token) ; Other IANA registered ; status ; These are the
participation statuses for a "VEVENT". Default is ; NEEDS-ACTION
partstatparam /= "PARTSTAT" "=" ("NEEDS-ACTION" ; To-do needs
action / "ACCEPTED" ; To-do accepted / "DECLINED" ; To-do declined
/ "TENTATIVE" ; To-do tentatively ; accepted / "DELEGATED" ; To-do
delegated / "COMPLETED" ; To-do completed. ; COMPLETED property has
;date/time completed. / "IN-PROCESS" ; To-do in process of ; being
completed / x-name ; Experimental status / iana-token) ; Other IANA
registered ; status ; These are the participation statuses for a
"VTODO". Default is ; NEEDS-ACTION partstatparam /= "PARTSTAT" "="
("NEEDS-ACTION" ; Journal needs action / "ACCEPTED" ; Journal
accepted / "DECLINED" ; Journal declined / x-name ; Experimental
status / iana-token) ; Other IANA registered ; status ; These are
the participation statuses for a "VJOURNAL". Default is ;
NEEDS-ACTION Description: This parameter can be specified on
properties with a CAL-ADDRESS value type. The parameter identifies
the participation status for the calendar user specified by the
property value. The parameter values differ depending on whether
they are associated with a group scheduled "VEVENT", "VTODO" or
"VJOURNAL". The values MUST match one of the values allowed for the
given calendar component. If not specified on a property that
allows this parameter, the default value is NEEDS-ACTION. Example:
ATTENDEE;PARTSTAT=DECLINED:MAILTO:jsmith@host.com Dawson &
Stenerson Standards Track [Page 26]
RFC 2445 iCalendar November
1998 4.2.13 Recurrence Identifier Range Parameter Name: RANGE
Purpose: To specify the effective range of recurrence instances
from the instance specified by the recurrence identifier specified
by the property. Format Definition: The property parameter is
defined by the following notation: rangeparam = "RANGE" "="
("THISANDPRIOR" ; To specify all instances prior to the recurrence
identifier / "THISANDFUTURE") ; To specify the instance specified
by the recurrence identifier ; and all subsequent recurrence
instances Description: The parameter can be specified on a property
that specifies a recurrence identifier. The parameter specifies the
effective range of recurrence instances that is specified by the
property. The effective range is from the recurrence identified
specified by the property. If this parameter is not specified an
allowed property, then the default range is the single instance
specified by the recurrence identifier value of the property. The
parameter value can be "THISANDPRIOR" to indicate a range defined
by the recurrence identified value of the property and all prior
instances. The parameter value can also be "THISANDFUTURE" to
indicate a range defined by the recurrence identifier and all
subsequent instances. Example:
RECURRENCE-ID;RANGE=THISANDPRIOR:19980401T133000Z 4.2.14 Alarm
Trigger Relationship Parameter Name: RELATED Purpose: To specify
the relationship of the alarm trigger with respect to the start or
end of the calendar component. Format Definition: The property
parameter is defined by the following notation: trigrelparam =
"RELATED" "=" ("START" ; Trigger off of start / "END") ; Trigger
off of end Dawson & Stenerson Standards Track [Page 27]
RFC 2445 iCalendar November 1998 Description: The parameter can be
specified on properties that specify an alarm trigger with a
DURATION value type. The parameter specifies whether the alarm will
trigger relative to the start or end of the calendar component. The
parameter value START will set the alarm to trigger off the start
of the calendar component; the parameter value END will set the
alarm to trigger off the end of the calendar component. If the
parameter is not specified on an allowable property, then the
default is START. Example: TRIGGER;RELATED=END:PT5M 4.2.15
Relationship Type Parameter Name: RELTYPE Purpose: To specify the
type of hierarchical relationship associated with the calendar
component specified by the property. Format Definition: The
property parameter is defined by the following notation:
reltypeparam = "RELTYPE" "=" ("PARENT" ; Parent relationship.
Default. / "CHILD" ; Child relationship / "SIBLING ; Sibling
relationship / iana-token ; Some other IANA registered ; iCalendar
relationship type / x-name) ; A non-standard, experimental ;
relationship type Description: This parameter can be specified on a
property that references another related calendar. The parameter
specifies the hierarchical relationship type of the calendar
component referenced by the property. The parameter value can be
PARENT, to indicate that the referenced calendar component is a
superior of calendar component; CHILD to indicate that the
referenced calendar component is a subordinate of the calendar
component; SIBLING to indicate that the referenced calendar
component is a peer of the calendar component. If this parameter is
not specified on an allowable property, the default relationship
type is PARENT. Example:
RELATED-TO;RELTYPE=SIBLING:<19960401-080045-4000F192713@host.com>
Dawson & Stenerson Standards Track [Page 28]
RFC 2445 iCalendar
November 1998 4.2.16 Participation Role Parameter Name: ROLE
Purpose: To specify the participation role for the calendar user
specified by the property. Format Definition: The property
parameter is defined by the following notation: roleparam = "ROLE"
"=" ("CHAIR" ; Indicates chair of the ; calendar entity /
"REQ-PARTICIPANT" ; Indicates a participant whose ; participation
is required / "OPT-PARTICIPANT" ; Indicates a participant whose ;
participation is optional / "NON-PARTICIPANT" ; Indicates a
participant who is ; copied for information ; purposes only /
x-name ; Experimental role / iana-token) ; Other IANA role ;
Default is REQ-PARTICIPANT Description: This parameter can be
specified on properties with a CAL-ADDRESS value type. The
parameter specifies the participation role for the calendar user
specified by the property in the group schedule calendar component.
If not specified on a property that allows this parameter, the
default value is REQ-PARTICIPANT. Example:
ATTENDEE;ROLE=CHAIR:MAILTO:mrbig@host.com 4.2.17 RSVP Expectation
Parameter Name: RSVP Purpose: To specify whether there is an
expectation of a favor of a reply from the calendar user specified
by the property value. Format Definition: The property parameter is
defined by the following notation: rsvpparam = "RSVP" "=" ("TRUE" /
"FALSE") ; Default is FALSE Dawson & Stenerson Standards Track
[Page 29]
RFC 2445 iCalendar November 1998 Description: This
parameter can be specified on properties with a CAL-ADDRESS value
type. The parameter identifies the expectation of a reply from the
calendar user specified by the property value. This parameter is
used by the "Organizer" to request a participation status reply
from an "Attendee" of a group scheduled event or to-do. If not
specified on a property that allows this parameter, the default
value is FALSE. Example: ATTENDEE;RSVP=TRUE:MAILTO:jsmith@host.com
4.2.18 Sent By Parameter Name: SENT-BY Purpose: To specify the
calendar user that is acting on behalf of the calendar user
specified by the property. Format Definition: The property
parameter is defined by the following notation: sentbyparam =
"SENT-BY" "=" DQUOTE cal-address DQUOTE Description: This parameter
can be specified on properties with a CAL-ADDRESS value type. The
parameter specifies the calendar user that is acting on behalf of
the calendar user specified by the property. The parameter value
MUST be a MAILTO URI as defined in [
RFC 1738]. The individual
calendar address parameter values MUST each be specified in a
quoted-string. Example:
ORGANIZER;SENT-BY:"MAILTO:sray@host.com":MAILTO:jsmith@host.com
4.2.19 Time Zone Identifier Parameter Name: TZID Purpose: To
specify the identifier for the time zone definition for a time
component in the property value. Format Definition: This property
parameter is defined by the following notation: tzidparam = "TZID"
"=" [tzidprefix] paramtext CRLF tzidprefix = "/" Dawson &
Stenerson Standards Track [Page 30]
RFC 2445 iCalendar November
1998 Description: The parameter MUST be specified on the "DTSTART",
"DTEND", "DUE", "EXDATE" and "RDATE" properties when either a DATE-
TIME or TIME value type is specified and when the value is not
either a UTC or a "floating" time. Refer to the DATE-TIME or TIME
value type definition for a description of UTC and "floating time"
formats. This property parameter specifies a text value which
uniquely identifies the "VTIMEZONE" calendar component to be used
when evaluating the time portion of the property. The value of the
TZID property parameter will be equal to the value of the TZID
property for the matching time zone definition. An individual
"VTIMEZONE" calendar component MUST be specified for each unique
"TZID" parameter value specified in the iCalendar object. The
parameter MUST be specified on properties with a DATE-TIME value if
the DATE-TIME is not either a UTC or a "floating" time. The
presence of the SOLIDUS character (US-ASCII decimal 47) as a
prefix, indicates that this TZID represents a unique ID in a
globally defined time zone registry (when such registry is
defined). Note: This document does not define a naming convention
for time zone identifiers. Implementers may want to use the naming
conventions defined in existing time zone specifications such as
the public-domain Olson database [TZ]. The specification of
globally unique time zone identifiers is not addressed by this
document and is left for future study. The following are examples
of this property parameter: DTSTART;TZID=US-Eastern:19980119T020000
DTEND;TZID=US-Eastern:19980119T030000 The TZID property parameter
MUST NOT be applied to DATE-TIME or TIME properties whose time
values are specified in UTC. The use of local time in a DATE-TIME
or TIME value without the TZID property parameter is to be
interpreted as a local time value, regardless of the existence of
"VTIMEZONE" calendar components in the iCalendar object. For more
information see the sections on the data types DATE-TIME and TIME.
Dawson & Stenerson Standards Track [Page 31]
RFC 2445 iCalendar
November 1998 4.2.20 Value Data Types Parameter Name: VALUE
Purpose: To explicitly specify the data type format for a property
value. Format Definition: The "VALUE" property parameter is defined
by the following notation: valuetypeparam = "VALUE" "=" valuetype
valuetype = ("BINARY" / "BOOLEAN" / "CAL-ADDRESS" / "DATE" /
"DATE-TIME" / "DURATION" / "FLOAT" / "INTEGER" / "PERIOD" / "RECUR"
/ "TEXT" / "TIME" / "URI" / "UTC-OFFSET" / x-name ; Some
experimental iCalendar data type. / iana-token) ; Some other IANA
registered iCalendar data type. Description: The parameter
specifies the data type and format of the property value. The
property values MUST be of a single value type. For example, a
"RDATE" property cannot have a combination of DATE- TIME and TIME
value types. If the property's value is the default value type,
then this parameter need not be specified. However, if the
property's default value type is overridden by some other allowable
value type, then this parameter MUST be specified. 4.3 Property
Value Data Types The properties in an iCalendar object are strongly
typed. The definition of each property restricts the value to be
one of the value data types, or simply value types, defined in this
section. The value type for a property will either be specified
implicitly as the default value type or will be explicitly
specified with the "VALUE" Dawson & Stenerson Standards Track
[Page 32]
RFC 2445 iCalendar November 1998 parameter. If the value
type of a property is one of the alternate valid types, then it
MUST be explicitly specified with the "VALUE" parameter. 4.3.1
Binary Value Name: BINARY Purpose: This value type is used to
identify properties that contain a character encoding of inline
binary data. For example, an inline attachment of an object code
might be included in an iCalendar object. Formal Definition: The
value type is defined by the following notation: binary =
*(4b-char) [b-end] ; A "BASE64" encoded character string, as
defined by [
RFC 2045]. b-end = (2b-char "==") / (3b-char "=")
b-char = ALPHA / DIGIT / "+" / "/" Description: Property values
with this value type MUST also include the inline encoding
parameter sequence of ";ENCODING=BASE64". That is, all inline
binary data MUST first be character encoded using the "BASE64"
encoding method defined in [
RFC 2045]. No additional content value
encoding (i.e., BACKSLASH character encoding) is defined for this
value type. Example: The following is an abridged example of a
"BASE64" encoded binary value data.
ATTACH;VALUE=BINARY;ENCODING=BASE64:MIICajCCAdOgAwIBAgICBEUwDQY
JKoZIhvcNAQEEBQAwdzELMAkGA1UEBhMCVVMxLDAqBgNVBAoTI05ldHNjYXBlI
ENvbW11bmljYXRpb25zIENvcnBvcmF0aW9uMRwwGgYDVQQLExNJbmZv
<...remainder of "BASE64" encoded binary data...> 4.3.2
Boolean Value Name: BOOLEAN Purpose: This value type is used to
identify properties that contain either a "TRUE" or "FALSE" Boolean
value. Formal Definition: The value type is defined by the
following notation: Dawson & Stenerson Standards Track [Page
33]
RFC 2445 iCalendar November 1998 boolean = "TRUE" / "FALSE"
Description: These values are case insensitive text. No additional
content value encoding (i.e., BACKSLASH character encoding) is
defined for this value type. Example: The following is an example
of a hypothetical property that has a BOOLEAN value type:
GIBBERISH:TRUE 4.3.3 Calendar User Address Value Name: CAL-ADDRESS
Purpose: This value type is used to identify properties that
contain a calendar user address. Formal Definition: The value type
is as defined by the following notation: cal-address = uri
Description: The value is a URI as defined by [
RFC 1738] or any
other IANA registered form for a URI. When used to address an
Internet email transport address for a calendar user, the value
MUST be a MAILTO URI, as defined by [
RFC 1738]. No additional
content value encoding (i.e., BACKSLASH character encoding) is
defined for this value type. Example:
ATTENDEE:MAILTO:jane_doe@host.com 4.3.4 Date Value Name: DATE
Purpose: This value type is used to identify values that contain a
calendar date. Formal Definition: The value type is defined by the
following notation: date = date-value date-value = date-fullyear
date-month date-mday date-fullyear = 4DIGIT Dawson & Stenerson
Standards Track [Page 34]
RFC 2445 iCalendar November 1998
date-month = 2DIGIT ;01-12 date-mday = 2DIGIT ;01-28, 01-29, 01-30,
01-31 ;based on month/year Description: If the property permits,
multiple "date" values are specified as a COMMA character (US-ASCII
decimal 44) separated list of values. The format for the value type
is expressed as the [ISO 8601] complete representation, basic
format for a calendar date. The textual format specifies a
four-digit year, two-digit month, and two-digit day of the month.
There are no separator characters between the year, month and day
component text. No additional content value encoding (i.e.,
BACKSLASH character encoding) is defined for this value type.
Example: The following represents July 14, 1997: 19970714 4.3.5
Date-Time Value Name: DATE-TIME Purpose: This value type is used to
identify values that specify a precise calendar date and time of
day. Formal Definition: The value type is defined by the following
notation: date-time = date "T" time ;As specified in the date and
time ;value definitions Description: If the property permits,
multiple "date-time" values are specified as a COMMA character
(US-ASCII decimal 44) separated list of values. No additional
content value encoding (i.e., BACKSLASH character encoding) is
defined for this value type. The "DATE-TIME" data type is used to
identify values that contain a precise calendar date and time of
day. The format is based on the [ISO 8601] complete representation,
basic format for a calendar date and time of day. The text format
is a concatenation of the "date", followed by the LATIN CAPITAL
LETTER T character (US-ASCII decimal 84) time designator, followed
by the "time" format. The "DATE-TIME" data type expresses time
values in three forms: The form of date and time with UTC offset
MUST NOT be used. For example, the following is not valid for a
date-time value: Dawson & Stenerson Standards Track [Page 35]
RFC 2445 iCalendar November 1998 DTSTART:19980119T230000-0800
;Invalid time format FORM #1: DATE WITH LOCAL TIME The date with
local time form is simply a date-time value that does not contain
the UTC designator nor does it reference a time zone. For example,
the following represents Janurary 18, 1998, at 11 PM:
DTSTART:19980118T230000 Date-time values of this type are said to
be "floating" and are not bound to any time zone in particular.
They are used to represent the same hour, minute, and second value
regardless of which time zone is currently being observed. For
example, an event can be defined that indicates that an individual
will be busy from 11:00 AM to 1:00 PM every day, no matter which
time zone the person is in. In these cases, a local time can be
specified. The recipient of an iCalendar object with a property
value consisting of a local time, without any relative time zone
information, SHOULD interpret the value as being fixed to whatever
time zone the ATTENDEE is in at any given moment. This means that
two ATTENDEEs, in different time zones, receiving the same event
definition as a floating time, may be participating in the event at
different actual times. Floating time SHOULD only be used where
that is the reasonable behavior. In most cases, a fixed time is
desired. To properly communicate a fixed time in a property value,
either UTC time or local time with time zone reference MUST be
specified. The use of local time in a DATE-TIME value without the
TZID property parameter is to be interpreted as floating time,
regardless of the existence of "VTIMEZONE" calendar components in
the iCalendar object. FORM #2: DATE WITH UTC TIME The date with UTC
time, or absolute time, is identified by a LATIN CAPITAL LETTER Z
suffix character (US-ASCII decimal 90), the UTC designator,
appended to the time value. For example, the following represents
January 19, 1998, at 0700 UTC: DTSTART:19980119T070000Z The TZID
property parameter MUST NOT be applied to DATE-TIME properties
whose time values are specified in UTC. FORM #3: DATE WITH LOCAL
TIME AND TIME ZONE REFERENCE Dawson & Stenerson Standards Track
[Page 36]
RFC 2445 iCalendar November 1998 The date and local time
with reference to time zone information is identified by the use
the TZID property parameter to reference the appropriate time zone
definition. TZID is discussed in detail in the section on Time
Zone. For example, the following represents 2 AM in New York on
Janurary 19, 1998: DTSTART;TZID=US-Eastern:19980119T020000 Example:
The following represents July 14, 1997, at 1:30 PM in New York City
in each of the three time formats, using the "DTSTART" property.
DTSTART:19970714T133000 ;Local time DTSTART:19970714T173000Z ;UTC
time DTSTART;TZID=US-Eastern:19970714T133000 ;Local time and time ;
zone reference A time value MUST ONLY specify 60 seconds when
specifying the periodic "leap second" in the time value. For
example: COMPLETED:19970630T235960Z 4.3.6 Duration Value Name:
DURATION Purpose: This value type is used to identify properties
that contain a duration of time. Formal Definition: The value type
is defined by the following notation: dur-value = (["+"] / "-") "P"
(dur-date / dur-time / dur-week) dur-date = dur-day [dur-time]
dur-time = "T" (dur-hour / dur-minute / dur-second) dur-week =
1*DIGIT "W" dur-hour = 1*DIGIT "H" [dur-minute] dur-minute =
1*DIGIT "M" [dur-second] dur-second = 1*DIGIT "S" dur-day = 1*DIGIT
"D" Description: If the property permits, multiple "duration"
values are specified by a COMMA character (US-ASCII decimal 44)
separated list of values. The format is expressed as the [ISO 8601]
basic format for the duration of time. The format can represent
durations in terms of weeks, days, hours, minutes, and seconds.
Dawson & Stenerson Standards Track [Page 37]
RFC 2445 iCalendar
November 1998 No additional content value encoding (i.e., BACKSLASH
character encoding) are defined for this value type. Example: A
duration of 15 days, 5 hours and 20 seconds would be: P15DT5H0M20S
A duration of 7 weeks would be: P7W 4.3.7 Float Value Name: FLOAT
Purpose: This value type is used to identify properties that
contain a real number value. Formal Definition: The value type is
defined by the following notation: float = (["+"] / "-") 1*DIGIT
["." 1*DIGIT] Description: If the property permits, multiple
"float" values are specified by a COMMA character (US-ASCII decimal
44) separated list of values. No additional content value encoding
(i.e., BACKSLASH character encoding) is defined for this value
type. Example: 1000000.0000001 1.333 -3.14 4.3.8 Integer Value
Name:INTEGER Purpose: This value type is used to identify
properties that contain a signed integer value. Formal Definition:
The value type is defined by the following notation: integer =
(["+"] / "-") 1*DIGIT Dawson & Stenerson Standards Track [Page
38]
RFC 2445 iCalendar November 1998 Description: If the property
permits, multiple "integer" values are specified by a COMMA
character (US-ASCII decimal 44) separated list of values. The valid
range for "integer" is -2147483648 to 2147483647. If the sign is
not specified, then the value is assumed to be positive. No
additional content value encoding (i.e., BACKSLASH character
encoding) is defined for this value type. Example: 1234567890
-1234567890 +1234567890 432109876 4.3.9 Period of Time Value Name:
PERIOD Purpose: This value type is used to identify values that
contain a precise period of time. Formal Definition: The data type
is defined by the following notation: period = period-explicit /
period-start period-explicit = date-time "/" date-time ; [ISO 8601]
complete representation basic format for a period of ; time
consisting of a start and end. The start MUST be before the ; end.
period-start = date-time "/" dur-value ; [ISO 8601] complete
representation basic format for a period of ; time consisting of a
start and positive duration of time. Description: If the property
permits, multiple "period" values are specified by a COMMA
character (US-ASCII decimal 44) separated list of values. There are
two forms of a period of time. First, a period of time is
identified by its start and its end. This format is expressed as
the [ISO 8601] complete representation, basic format for
"DATE-TIME" start of the period, followed by a SOLIDUS character
(US-ASCII decimal 47), followed by the "DATE-TIME" of the end of
the period. The start of the period MUST be before the end of the
period. Second, a period of time can also be defined by a start and
a positive duration of time. The format is expressed as the [ISO
8601] complete representation, basic format for the "DATE-TIME"
start of Dawson & Stenerson Standards Track [Page 39]
RFC 2445
iCalendar November 1998 the period, followed by a SOLIDUS character
(US-ASCII decimal 47), followed by the [ISO 8601] basic format for
"DURATION" of the period. Example: The period starting at 18:00:00
UTC, on January 1, 1997 and ending at 07:00:00 UTC on January 2,
1997 would be: 19970101T180000Z/19970102T070000Z The period start
at 18:00:00 on January 1, 1997 and lasting 5 hours and 30 minutes
would be: 19970101T180000Z/PT5H30M No additional content value
encoding (i.e., BACKSLASH character encoding) is defined for this
value type. 4.3.10 Recurrence Rule Value Name: RECUR Purpose: This
value type is used to identify properties that contain a recurrence
rule specification. Formal Definition: The value type is defined by
the following notation: recur = "FREQ"=freq *( ; either UNTIL or
COUNT may appear in a 'recur', ; but UNTIL and COUNT MUST NOT occur
in the same 'recur' ( ";" "UNTIL" "=" enddate ) / ( ";" "COUNT" "="
1*DIGIT ) / ; the rest of these keywords are optional, ; but MUST
NOT occur more than once ( ";" "INTERVAL" "=" 1*DIGIT ) / ( ";"
"BYSECOND" "=" byseclist ) / ( ";" "BYMINUTE" "=" byminlist ) / (
";" "BYHOUR" "=" byhrlist ) / ( ";" "BYDAY" "=" bywdaylist ) / (
";" "BYMONTHDAY" "=" bymodaylist ) / ( ";" "BYYEARDAY" "="
byyrdaylist ) / ( ";" "BYWEEKNO" "=" bywknolist ) / ( ";" "BYMONTH"
"=" bymolist ) / ( ";" "BYSETPOS" "=" bysplist ) / ( ";" "WKST" "="
weekday ) / Dawson & Stenerson Standards Track [Page 40]
RFC 2445 iCalendar November 1998 ( ";" x-name "=" text ) ) freq =
"SECONDLY" / "MINUTELY" / "HOURLY" / "DAILY" / "WEEKLY" / "MONTHLY"
/ "YEARLY" enddate = date enddate =/ date-time ;An UTC value
byseclist = seconds / ( seconds *("," seconds) ) seconds = 1DIGIT /
2DIGIT ;0 to 59 byminlist = minutes / ( minutes *("," minutes) )
minutes = 1DIGIT / 2DIGIT ;0 to 59 byhrlist = hour / ( hour *(","
hour) ) hour = 1DIGIT / 2DIGIT ;0 to 23 bywdaylist = weekdaynum / (
weekdaynum *("," weekdaynum) ) weekdaynum = [([plus] ordwk / minus
ordwk)] weekday plus = "+" minus = "-" ordwk = 1DIGIT / 2DIGIT ;1
to 53 weekday = "SU" / "MO" / "TU" / "WE" / "TH" / "FR" / "SA"
;Corresponding to SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY,
;FRIDAY, SATURDAY and SUNDAY days of the week. bymodaylist =
monthdaynum / ( monthdaynum *("," monthdaynum) ) monthdaynum =
([plus] ordmoday) / (minus ordmoday) ordmoday = 1DIGIT / 2DIGIT ;1
to 31 byyrdaylist = yeardaynum / ( yeardaynum *("," yeardaynum) )
yeardaynum = ([plus] ordyrday) / (minus ordyrday) ordyrday = 1DIGIT
/ 2DIGIT / 3DIGIT ;1 to 366 bywknolist = weeknum / ( weeknum *(","
weeknum) ) Dawson & Stenerson Standards Track [Page 41]
RFC 2445 iCalendar November 1998 weeknum = ([plus] ordwk) / (minus
ordwk) bymolist = monthnum / ( monthnum *("," monthnum) ) monthnum
= 1DIGIT / 2DIGIT ;1 to 12 bysplist = setposday / ( setposday *(","
setposday) ) setposday = yeardaynum Description: If the property
permits, multiple "recur" values are specified by a COMMA character
(US-ASCII decimal 44) separated list of values. The value type is a
structured value consisting of a list of one or more recurrence
grammar parts. Each rule part is defined by a NAME=VALUE pair. The
rule parts are separated from each other by the SEMICOLON character
(US-ASCII decimal 59). The rule parts are not ordered in any
particular sequence. Individual rule parts MUST only be specified
once. The FREQ rule part identifies the type of recurrence rule.
This rule part MUST be specified in the recurrence rule. Valid
values include SECONDLY, to specify repeating events based on an
interval of a second or more; MINUTELY, to specify repeating events
based on an interval of a minute or more; HOURLY, to specify
repeating events based on an interval of an hour or more; DAILY, to
specify repeating events based on an interval of a day or more;
WEEKLY, to specify repeating events based on an interval of a week
or more; MONTHLY, to specify repeating events based on an interval
of a month or more; and YEARLY, to specify repeating events based
on an interval of a year or more. The INTERVAL rule part contains a
positive integer representing how often the recurrence rule
repeats. The default value is "1", meaning every second for a
SECONDLY rule, or every minute for a MINUTELY rule, every hour for
an HOURLY rule, every day for a DAILY rule, every week for a WEEKLY
rule, every month for a MONTHLY rule and every year for a YEARLY
rule. The UNTIL rule part defines a date-time value which bounds
the recurrence rule in an inclusive manner. If the value specified
by UNTIL is synchronized with the specified recurrence, this date
or date-time becomes the last instance of the recurrence. If
specified as a date-time value, then it MUST be specified in an UTC
time format. If not present, and the COUNT rule part is also not
present, the RRULE is considered to repeat forever. The COUNT rule
part defines the number of occurrences at which to range-bound the
recurrence. The "DTSTART" property value, if Dawson & Stenerson
Standards Track [Page 42]
RFC 2445 iCalendar November 1998
specified, counts as the first occurrence. The BYSECOND rule part
specifies a COMMA character (US-ASCII decimal 44) separated list of
seconds within a minute. Valid values are 0 to 59. The BYMINUTE
rule part specifies a COMMA character (US-ASCII decimal 44)
separated list of minutes within an hour. Valid values are 0 to 59.
The BYHOUR rule part specifies a COMMA character (US- ASCII decimal
44) separated list of hours of the day. Valid values are 0 to 23.
The BYDAY rule part specifies a COMMA character (US-ASCII decimal
44) separated list of days of the week; MO indicates Monday; TU
indicates Tuesday; WE indicates Wednesday; TH indicates Thursday;
FR indicates Friday; SA indicates Saturday; SU indicates Sunday.
Each BYDAY value can also be preceded by a positive (+n) or
negative (-n) integer. If present, this indicates the nth
occurrence of the specific day within the MONTHLY or YEARLY RRULE.
For example, within a MONTHLY rule, +1MO (or simply 1MO) represents
the first Monday within the month, whereas -1MO represents the last
Monday of the month. If an integer modifier is not present, it
means all days of this type within the specified frequency. For
example, within a MONTHLY rule, MO represents all Mondays within
the month. The BYMONTHDAY rule part specifies a COMMA character
(ASCII decimal 44) separated list of days of the month. Valid
values are 1 to 31 or -31 to -1. For example, -10 represents the
tenth to the last day of the month. The BYYEARDAY rule part
specifies a COMMA character (US-ASCII decimal 44) separated list of
days of the year. Valid values are 1 to 366 or -366 to -1. For
example, -1 represents the last day of the year (December 31st) and
-306 represents the 306th to the last day of the year (March 1st).
The BYWEEKNO rule part specifies a COMMA character (US-ASCII
decimal 44) separated list of ordinals specifying weeks of the
year. Valid values are 1 to 53 or -53 to -1. This corresponds to
weeks according to week numbering as defined in [ISO 8601]. A week
is defined as a seven day period, starting on the day of the week
defined to be the week start (see WKST). Week number one of the
calendar year is the first week which contains at least four (4)
days in that calendar year. This rule part is only valid for YEARLY
rules. For example, 3 represents the third week of the year. Note:
Assuming a Monday week start, week 53 can only occur when Thursday
is January 1 or if it is a leap year and Wednesday is January 1.
Dawson & Stenerson Standards Track [Page 43]
RFC 2445 iCalendar
November 1998 The BYMONTH rule part specifies a COMMA character
(US-ASCII decimal 44) separated list of months of the year. Valid
values are 1 to 12. The WKST rule part specifies the day on which
the workweek starts. Valid values are MO, TU, WE, TH, FR, SA and
SU. This is significant when a WEEKLY RRULE has an interval greater
than 1, and a BYDAY rule part is specified. This is also
significant when in a YEARLY RRULE when a BYWEEKNO rule part is
specified. The default value is MO. The BYSETPOS rule part
specifies a COMMA character (US-ASCII decimal 44) separated list of
values which corresponds to the nth occurrence within the set of
events specified by the rule. Valid values are 1 to 366 or -366 to
-1. It MUST only be used in conjunction with another BYxxx rule
part. For example "the last work day of the month" could be
represented as: RRULE:FREQ=MONTHLY;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=-1
Each BYSETPOS value can include a positive (+n) or negative (-n)
integer. If present, this indicates the nth occurrence of the
specific occurrence within the set of events specified by the rule.
If BYxxx rule part values are found which are beyond the available
scope (ie, BYMONTHDAY=30 in February), they are simply ignored.
Information, not contained in the rule, necessary to determine the
various recurrence instance start time and dates are derived from
the Start Time (DTSTART) entry attribute. For example,
"FREQ=YEARLY;BYMONTH=1" doesn't specify a specific day within the
month or a time. This information would be the same as what is
specified for DTSTART. BYxxx rule parts modify the recurrence in
some manner. BYxxx rule parts for a period of time which is the
same or greater than the frequency generally reduce or limit the
number of occurrences of the recurrence generated. For example,
"FREQ=DAILY;BYMONTH=1" reduces the number of recurrence instances
from all days (if BYMONTH tag is not present) to all days in
January. BYxxx rule parts for a period of time less than the
frequency generally increase or expand the number of occurrences of
the recurrence. For example, "FREQ=YEARLY;BYMONTH=1,2" increases
the number of days within the yearly recurrence set from 1 (if
BYMONTH tag is not present) to 2. If multiple BYxxx rule parts are
specified, then after evaluating the specified FREQ and INTERVAL
rule parts, the BYxxx rule parts are applied to the current set of
evaluated occurrences in the following order: BYMONTH, BYWEEKNO,
BYYEARDAY, BYMONTHDAY, BYDAY, BYHOUR, BYMINUTE, BYSECOND and
BYSETPOS; then COUNT and UNTIL are evaluated. Dawson &
Stenerson Standards Track [Page 44]
RFC 2445 iCalendar November
1998 Here is an example of evaluating multiple BYxxx rule parts.
DTSTART;TZID=US-Eastern:19970105T083000
RRULE:FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;
BYMINUTE=30 First, the "INTERVAL=2" would be applied to
"FREQ=YEARLY" to arrive at "every other year". Then, "BYMONTH=1"
would be applied to arrive at "every January, every other year".
Then, "BYDAY=SU" would be applied to arrive at "every Sunday in
January, every other year". Then, "BYHOUR=8,9" would be applied to
arrive at "every Sunday in January at 8 AM and 9 AM, every other
year". Then, "BYMINUTE=30" would be applied to arrive at "every
Sunday in January at 8:30 AM and 9:30 AM, every other year". Then,
lacking information from RRULE, the second is derived from DTSTART,
to end up in "every Sunday in January at 8:30:00 AM and 9:30:00 AM,
every other year". Similarly, if the BYMINUTE, BYHOUR, BYDAY,
BYMONTHDAY or BYMONTH rule part were missing, the appropriate
minute, hour, day or month would have been retrieved from the
"DTSTART" property. No additional content value encoding (i.e.,
BACKSLASH character encoding) is defined for this value type.
Example: The following is a rule which specifies 10 meetings which
occur every other day: FREQ=DAILY;COUNT=10;INTERVAL=2 There are
other examples specified in the "RRULE" specification. 4.3.11 Text
Value Name: TEXT Purpose This value type is used to identify values
that contain human readable text. Formal Definition: The character
sets supported by this revision of iCalendar are UTF-8 and US ASCII
thereof. The applicability to other character sets is for future
work. The value type is defined by the following notation. text =
*(TSAFE-CHAR / ":" / DQUOTE / ESCAPED-CHAR) ; Folded according to
description above ESCAPED-CHAR = "\\" / "\;" / "\," / "\N" / "\n")
; \\ encodes \, \N or \n encodes newline ; \; encodes ;, \, encodes
, Dawson & Stenerson Standards Track [Page 45]
RFC 2445
iCalendar November 1998 TSAFE-CHAR = %x20-21 / %x23-2B / %x2D-39 /
%x3C-5B %x5D-7E / NON-US-ASCII ; Any character except CTLs not
needed by the current ; character set, DQUOTE, ";", ":", "\", ","
Note: Certain other character sets may require modification of the
above definitions, but this is beyond the scope of this document.
Description: If the property permits, multiple "text" values are
specified by a COMMA character (US-ASCII decimal 44) separated list
of values. The language in which the text is represented can be
controlled by the "LANGUAGE" property parameter. An intentional
formatted text line break MUST only be included in a "TEXT"
property value by representing the line break with the character
sequence of BACKSLASH (US-ASCII decimal 92), followed by a LATIN
SMALL LETTER N (US-ASCII decimal 110) or a LATIN CAPITAL LETTER N
(US-ASCII decimal 78), that is "\n" or "\N". The "TEXT" property
values may also contain special characters that are used to signify
delimiters, such as a COMMA character for lists of values or a
SEMICOLON character for structured values. In order to support the
inclusion of these special characters in "TEXT" property values,
they MUST be escaped with a BACKSLASH character. A BACKSLASH
character (US-ASCII decimal 92) in a "TEXT" property value MUST be
escaped with another BACKSLASH character. A COMMA character in a
"TEXT" property value MUST be escaped with a BACKSLASH character
(US-ASCII decimal 92). A SEMICOLON character in a "TEXT" property
value MUST be escaped with a BACKSLASH character (US-ASCII decimal
92). However, a COLON character in a "TEXT" property value SHALL
NOT be escaped with a BACKSLASH character.Example: A multiple line
value of: Project XYZ Final Review Conference Room - 3B Come
Prepared. would be represented as: Project XYZ Final
Review\nConference Room - 3B\nCome Prepared. Dawson & Stenerson
Standards Track [Page 46]
RFC 2445 iCalendar November 1998 4.3.12
Time Value Name: TIME Purpose: This value type is used to identify
values that contain a time of day. Formal Definition: The data type
is defined by the following notation: time = time-hour time-minute
time-second [time-utc] time-hour = 2DIGIT ;00-23 time-minute =
2DIGIT ;00-59 time-second = 2DIGIT ;00-60 ;The "60" value is used
to account for "leap" seconds. time-utc = "Z" Description: If the
property permits, multiple "time" values are specified by a COMMA
character (US-ASCII decimal 44) separated list of values. No
additional content value encoding (i.e., BACKSLASH character
encoding) is defined for this value type. The "TIME" data type is
used to identify values that contain a time of day. The format is
based on the [ISO 8601] complete representation, basic format for a
time of day. The text format consists of a two-digit 24-hour of the
day (i.e., values 0-23), two- digit minute in the hour (i.e.,
values 0-59), and two-digit seconds in the minute (i.e., values
0-60). The seconds value of 60 MUST only to be used to account for
"leap" seconds. Fractions of a second are not supported by this
format. In parallel to the "DATE-TIME" definition above, the "TIME"
data type expresses time values in three forms: The form of time
with UTC offset MUST NOT be used. For example, the following is NOT
VALID for a time value: 230000-0800 ;Invalid time format FORM #1
LOCAL TIME The local time form is simply a time value that does not
contain the UTC designator nor does it reference a time zone. For
example, 11:00 PM: 230000 Dawson & Stenerson Standards Track
[Page 47]
RFC 2445 iCalendar November 1998 Time values of this type
are said to be "floating" and are not bound to any time zone in
particular. They are used to represent the same hour, minute, and
second value regardless of which time zone is currently being
observed. For example, an event can be defined that indicates that
an individual will be busy from 11:00 AM to 1:00 PM every day, no
matter which time zone the person is in. In these cases, a local
time can be specified. The recipient of an iCalendar object with a
property value consisting of a local time, without any relative
time zone information, SHOULD interpret the value as being fixed to
whatever time zone the ATTENDEE is in at any given moment. This
means that two ATTENDEEs may participate in the same event at
different UTC times; floating time SHOULD only be used where that
is reasonable behavior. In most cases, a fixed time is desired. To
properly communicate a fixed time in a property value, either UTC
time or local time with time zone reference MUST be specified. The
use of local time in a TIME value without the TZID property
parameter is to be interpreted as a local time value, regardless of
the existence of "VTIMEZONE" calendar components in the iCalendar
object. FORM #2: UTC TIME UTC time, or absolute time, is identified
by a LATIN CAPITAL LETTER Z suffix character (US-ASCII decimal 90),
the UTC designator, appended to the time value. For example, the
following represents 07:00 AM UTC: 070000Z The TZID property
parameter MUST NOT be applied to TIME properties whose time values
are specified in UTC. FORM #3: LOCAL TIME AND TIME ZONE REFERENCE
The local time with reference to time zone information form is
identified by the use the TZID property parameter to reference the
appropriate time zone definition. TZID is discussed in detail in
the section on Time Zone. Example: The following represents 8:30 AM
in New York in Winter, five hours behind UTC, in each of the three
formats using the "X- TIMEOFDAY" non-standard property: Dawson
& Stenerson Standards Track [Page 48]
RFC 2445 iCalendar
November 1998 X-TIMEOFDAY:083000 X-TIMEOFDAY:133000Z
X-TIMEOFDAY;TZID=US-Eastern:083000 4.3.13 URI Value Name: URI
Purpose: This value type is used to identify values that contain a
uniform resource identifier (URI) type of reference to the property
value. Formal Definition: The data type is defined by the following
notation: uri = 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: Dawson &
Stenerson Standards Track [Page 49]
RFC 2445 iCalendar November
1998 utc-offset = time-numzone ;As defined above in time data type
time-numzone = ("+" / "-") time-hour time-minute [time- second]
Description: The PLUS SIGN character MUST be specified for positive
UTC offsets (i.e., ahead of UTC). The value of "-0000" and
"-000000" are not allowed. The time-second, if present, may not be
60; if absent, it defaults to zero. No additional content value
encoding (i.e., BACKSLASH character encoding) is defined for this
value type. Example: The following UTC offsets are given for
standard time for New York (five hours behind UTC) and Geneva (one
hour ahead of UTC): -0500 +0100 4.4 iCalendar Object The
Calendaring and Scheduling Core Object is a collection of
calendaring and scheduling information. Typically, this information
will consist of a single iCalendar object. However, multiple
iCalendar objects can be sequentially grouped together. The first
line and last line of the iCalendar object MUST contain a pair of
iCalendar object delimiter strings. The syntax for an iCalendar
object is as follows: icalobject = 1*("BEGIN" ":" "VCALENDAR" CRLF
icalbody "END" ":" "VCALENDAR" CRLF) The following is a simple
example of an iCalendar object: BEGIN:VCALENDAR VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN BEGIN:VEVENT
DTSTART:19970714T170000Z DTEND:19970715T035959Z SUMMARY:Bastille
Day Party END:VEVENT END:VCALENDAR Dawson & Stenerson Standards
Track [Page 50]
RFC 2445 iCalendar November 1998 4.5 Property A
property is the definition of an individual attribute describing a
calendar or a calendar component. A property takes the form defined
by the "contentline" notation defined in section 4.1.1. The
following is an example of a property: DTSTART:19960415T133000Z
This memo imposes no ordering of properties within an iCalendar
object. Property names, parameter names and enumerated parameter
values are case insensitive. For example, the property name "DUE"
is the same as "due" and "Due",
DTSTART;TZID=US-Eastern:19980714T120000 is the same as
DtStart;TzID=US-Eastern:19980714T120000. 4.6 Calendar Components
The body of the iCalendar object consists of a sequence of calendar
properties and one or more calendar components. The calendar
properties are attributes that apply to the calendar as a whole.
The calendar components are collections of properties that express
a particular calendar semantic. For example, the calendar component
can specify an event, a to-do, a journal entry, time zone
information, or free/busy time information, or an alarm. The body
of the iCalendar object is defined by the following notation:
icalbody = calprops component calprops = 2*( ; 'prodid' and
'version' are both REQUIRED, ; but MUST NOT occur more than once
prodid /version / ; 'calscale' and 'method' are optional, ; but
MUST NOT occur more than once calscale / method / x-prop Dawson
& Stenerson Standards Track [Page 51]
RFC 2445 iCalendar
November 1998 ) component = 1*(eventc / todoc / journalc /
freebusyc / / timezonec / iana-comp / x-comp) iana-comp = "BEGIN"
":" iana-token CRLF 1*contentline "END" ":" iana-token CRLF x-comp
= "BEGIN" ":" x-name CRLF 1*contentline "END" ":" x-name CRLF An
iCalendar object MUST include the "PRODID" and "VERSION" calendar
properties. In addition, it MUST include at least one calendar
component. Special forms of iCalendar objects are possible to
publish just busy time (i.e., only a "VFREEBUSY" calendar
component) or time zone (i.e., only a "VTIMEZONE" calendar
component) information. In addition, a complex iCalendar object is
possible that is used to capture a complete snapshot of the
contents of a calendar (e.g., composite of many different calendar
components). More commonly, an iCalendar object will consist of
just a single "VEVENT", "VTODO" or "VJOURNAL" calendar component.
4.6.1 Event Component Component Name: "VEVENT" Purpose: Provide a
grouping of component properties that describe an event. Format
Definition: A "VEVENT" calendar component is defined by the
following notation: eventc = "BEGIN" ":" "VEVENT" CRLF eventprop
*alarmc "END" ":" "VEVENT" CRLF eventprop = *( ; the following are
optional, ; but MUST NOT occur more than once class / created /
description / dtstart / geo / Dawson & Stenerson Standards
Track [Page 52]
RFC 2445 iCalendar November 1998 last-mod /
location / organizer / priority / dtstamp / seq / status / summary
/ transp / uid / url / recurid / ; either 'dtend' or 'duration' may
appear in ; a 'eventprop', but 'dtend' and 'duration' ; MUST NOT
occur in the same 'eventprop' dtend / duration / ; the following
are optional, ; and MAY occur more than once attach / attendee /
categories / comment / contact / exdate / exrule / rstatus /
related / resources / rdate / rrule / x-prop ) Description: A
"VEVENT" calendar component is a grouping of component properties,
and possibly including "VALARM" calendar components, that
represents a scheduled amount of time on a calendar. For example,
it can be an activity; such as a one-hour long, department meeting
from 8:00 AM to 9:00 AM, tomorrow. Generally, an event will take up
time on an individual calendar. Hence, the event will appear as an
opaque interval in a search for busy time. Alternately, the event
can have its Time Transparency set to "TRANSPARENT" in order to
prevent blocking of the event in searches for busy time. The
"VEVENT" is also the calendar component used to specify an
anniversary or daily reminder within a calendar. These events have
a DATE value type for the "DTSTART" property instead of the default
data type of DATE-TIME. If such a "VEVENT" has a "DTEND" property,
it MUST be specified as a DATE value also. The anniversary type of
"VEVENT" can span more than one date (i.e, "DTEND" property value
is set to a calendar date after the "DTSTART" property value). The
"DTSTART" property for a "VEVENT" specifies the inclusive start of
the event. For recurring events, it also specifies the very first
instance in the recurrence set. The "DTEND" property for a "VEVENT"
calendar component specifies the non-inclusive end of the event.
For cases where a "VEVENT" calendar component specifies a "DTSTART"
property with a DATE data type but no "DTEND" property, the events
non-inclusive end is the end of the calendar date specified by the
"DTSTART" property. For cases where a "VEVENT" calendar component
specifies a "DTSTART" property with a DATE-TIME data type but no
"DTEND" property, the event ends on the same calendar date and time
of day specified by the "DTSTART" property. Dawson & Stenerson
Standards Track [Page 53]
RFC 2445 iCalendar November 1998 The
"VEVENT" calendar component cannot be nested within another
calendar component. However, "VEVENT" calendar components can be
related to each other or to a "VTODO" or to a "VJOURNAL" calendar
component with the "RELATED-TO" property. Example: The following is
an example of the "VEVENT" calendar component used to represent a
meeting that will also be opaque to searches for busy time:
BEGIN:VEVENT UID:19970901T130000Z-123401@host.com
DTSTAMP:19970901T1300Z DTSTART:19970903T163000Z
DTEND:19970903T190000Z SUMMARY:Annual Employee Review CLASS:PRIVATE
CATEGORIES:BUSINESS,HUMAN RESOURCES END:VEVENT The following is an
example of the "VEVENT" calendar component used to represent a
reminder that will not be opaque, but rather transparent, to
searches for busy time: BEGIN:VEVENT
UID:19970901T130000Z-123402@host.com DTSTAMP:19970901T1300Z
DTSTART:19970401T163000Z DTEND:19970402T010000Z SUMMARY:Laurel is
in sensitivity awareness class. CLASS:PUBLIC
CATEGORIES:BUSINESS,HUMAN RESOURCES TRANSP:TRANSPARENT END:VEVENT
The following is an example of the "VEVENT" calendar component used
to represent an anniversary that will occur annually. Since it
takes up no time, it will not appear as opaque in a search for busy
time; no matter what the value of the "TRANSP" property indicates:
BEGIN:VEVENT UID:19970901T130000Z-123403@host.com
DTSTAMP:19970901T1300Z DTSTART:19971102 SUMMARY:Our Blissful
Anniversary CLASS:CONFIDENTIAL
CATEGORIES:ANNIVERSARY,PERSONAL,SPECIAL OCCASION RRULE:FREQ=YEARLY
END:VEVENT Dawson & Stenerson Standards Track [Page 54]
RFC 2445 iCalendar November 1998 4.6.2 To-do Component Component Name:
VTODO Purpose: Provide a grouping of calendar properties that
describe a to-do. Formal Definition: A "VTODO" calendar component
is defined by the following notation: todoc = "BEGIN" ":" "VTODO"
CRLF todoprop *alarmc "END" ":" "VTODO" CRLF todoprop = *( ; the
following are optional, ; but MUST NOT occur more than once class /
completed / created / description / dtstamp / dtstart / geo /
last-mod / location / organizer / percent / priority / recurid /
seq / status / summary / uid / url / ; either 'due' or 'duration'
may appear in ; a 'todoprop', but 'due' and 'duration' ; MUST NOT
occur in the same 'todoprop' due / duration / ; the following are
optional, ; and MAY occur more than once attach / attendee /
categories / comment / contact / exdate / exrule / rstatus /
related / resources / rdate / rrule / x-prop ) Description: A
"VTODO" calendar component is a grouping of component properties
and possibly "VALARM" calendar components that represent an
action-item or assignment. For example, it can be used to represent
an item of work assigned to an individual; such as "turn in travel
expense today". The "VTODO" calendar component cannot be nested
within another calendar component. However, "VTODO" calendar
components can be related to each other or to a "VTODO" or to a
"VJOURNAL" calendar component with the "RELATED-TO" property.
Dawson & Stenerson Standards Track [Page 55]
RFC 2445 iCalendar
November 1998 A "VTODO" calendar component without the "DTSTART"
and "DUE" (or "DURATION") properties specifies a to-do that will be
associated with each successive calendar date, until it is
completed. Example: The following is an example of a "VTODO"
calendar component: BEGIN:VTODO
UID:19970901T130000Z-123404@host.com DTSTAMP:19970901T1300Z
DTSTART:19970415T133000Z DUE:19970416T045959Z SUMMARY:1996 Income
Tax Preparation CLASS:CONFIDENTIAL CATEGORIES:FAMILY,FINANCE
PRIORITY:1 STATUS:NEEDS-ACTION END:VTODO 4.6.3 Journal Component
Component Name: VJOURNAL Purpose: Provide a grouping of component
properties that describe a journal entry. Formal Definition: A
"VJOURNAL" calendar component is defined by the following notation:
journalc = "BEGIN" ":" "VJOURNAL" CRLF jourprop "END" ":"
"VJOURNAL" CRLF jourprop = *( ; the following are optional, ; but
MUST NOT occur more than once class / created / description /
dtstart / dtstamp / last-mod / organizer / recurid / seq / status /
summary / uid / url / ; the following are optional, ; and MAY occur
more than once attach / attendee / categories / comment / contact /
exdate / exrule / related / rdate / rrule / rstatus / x-prop Dawson
& Stenerson Standards Track [Page 56]
RFC 2445 iCalendar
November 1998 ) Description: A "VJOURNAL" calendar component is a
grouping of component properties that represent one or more
descriptive text notes associated with a particular calendar date.
The "DTSTART" property is used to specify the calendar date that
the journal entry is associated with. Generally, it will have a
DATE value data type, but it can also be used to specify a
DATE-TIME value data type. Examples of a journal entry include a
daily record of a legislative body or a journal entry of individual
telephone contacts for the day or an ordered list of
accomplishments for the day. The "VJOURNAL" calendar component can
also be used to associate a document with a calendar date. The
"VJOURNAL" calendar component does not take up time on a calendar.
Hence, it does not play a role in free or busy time searches - - it
is as though it has a time transparency value of TRANSPARENT. It is
transparent to any such searches. The "VJOURNAL" calendar component
cannot be nested within another calendar component. However,
"VJOURNAL" calendar components can be related to each other or to a
"VEVENT" or to a "VTODO" calendar component, with the "RELATED-TO"
property. Example: The following is an example of the "VJOURNAL"
calendar component: BEGIN:VJOURNAL
UID:19970901T130000Z-123405@host.com DTSTAMP:19970901T1300Z
DTSTART;VALUE=DATE:19970317 SUMMARY:Staff meeting minutes
DESCRIPTION:1. Staff meeting: Participants include Joe\, Lisa and
Bob. Aurora project plans were reviewed. There is currently no
budget reserves for this project. Lisa will escalate to management.
Next meeting on Tuesday.\n 2. Telephone Conference: ABC Corp. sales
representative called to discuss new printer. Promised to get us a
demo by Friday.\n 3. Henry Miller (Handsoff Insurance): Car was
totaled by tree. Is looking into a loaner car. 654-2323 (tel).
END:VJOURNAL Dawson & Stenerson Standards Track [Page 57]
RFC 2445 iCalendar November 1998 4.6.4 Free/Busy Component Component
Name: VFREEBUSY Purpose: Provide a grouping of component properties
that describe either a request for free/busy time, describe a
response to a request for free/busy time or describe a published
set of busy time. Formal Definition: A "VFREEBUSY" calendar
component is defined by the following notation: freebusyc = "BEGIN"
":" "VFREEBUSY" CRLF fbprop "END" ":" "VFREEBUSY" CRLF fbprop = *(
; the following are optional, ; but MUST NOT occur more than once
contact / dtstart / dtend / duration / dtstamp / organizer / uid /
url / ; the following are optional, ; and MAY occur more than once
attendee / comment / freebusy / rstatus / x-prop ) Description: A
"VFREEBUSY" calendar component is a grouping of component
properties that represents either a request for, a reply to a
request for free or busy time information or a published set of
busy time information. When used to request free/busy time
information, the "ATTENDEE" property specifies the calendar users
whose free/busy time is being requested; the "ORGANIZER" property
specifies the calendar user who is requesting the free/busy time;
the "DTSTART" and "DTEND" properties specify the window of time for
which the free/busy time is being requested; the "UID" and
"DTSTAMP" properties are specified to assist in proper sequencing
of multiple free/busy time requests. When used to reply to a
request for free/busy time, the "ATTENDEE" property specifies the
calendar user responding to the free/busy time request; the
"ORGANIZER" property specifies the calendar user that originally
requested the free/busy time; the "FREEBUSY" property specifies the
free/busy time information (if it exists); and the Dawson &
Stenerson Standards Track [Page 58]
RFC 2445 iCalendar November
1998 "UID" and "DTSTAMP" properties are specified to assist in
proper sequencing of multiple free/busy time replies. When used to
publish busy time, the "ORGANIZER" property specifies the calendar
user associated with the published busy time; the "DTSTART" and
"DTEND" properties specify an inclusive time window that surrounds
the busy time information; the "FREEBUSY" property specifies the
published busy time information; and the "DTSTAMP" property
specifies the date/time that iCalendar object was created. The
"VFREEBUSY" calendar component cannot be nested within another
calendar component. Multiple "VFREEBUSY" calendar components can be
specified within an iCalendar object. This permits the grouping of
Free/Busy information into logical collections, such as monthly
groups of busy time information. The "VFREEBUSY" calendar component
is intended for use in iCalendar object methods involving requests
for free time, requests for busy time, requests for both free and
busy, and the associated replies. Free/Busy information is
represented with the "FREEBUSY" property. This property provides a
terse representation of time periods. One or more "FREEBUSY"
properties can be specified in the "VFREEBUSY" calendar component.
When present in a "VFREEBUSY" calendar component, the "DTSTART" and
"DTEND" properties SHOULD be specified prior to any "FREEBUSY"
properties. In a free time request, these properties can be used in
combination with the "DURATION" property to represent a request for
a duration of free time within a specified window of time. The
recurrence properties ("RRULE", "EXRULE", "RDATE", "EXDATE") are
not permitted within a "VFREEBUSY" calendar component. Any
recurring events are resolved into their individual busy time
periods using the "FREEBUSY" property. Example: The following is an
example of a "VFREEBUSY" calendar component used to request free or
busy time information: BEGIN:VFREEBUSY
ORGANIZER:MAILTO:jane_doe@host1.com
ATTENDEE:MAILTO:john_public@host2.com DTSTART:19971015T050000Z
DTEND:19971016T050000Z DTSTAMP:19970901T083000Z END:VFREEBUSY
Dawson & Stenerson Standards Track [Page 59]
RFC 2445 iCalendar
November 1998 The following is an example of a "VFREEBUSY" calendar
component used to reply to the request with busy time information:
BEGIN:VFREEBUSY ORGANIZER:MAILTO:jane_doe@host1.com
ATTENDEE:MAILTO:john_public@host2.com DTSTAMP:19970901T100000Z
FREEBUSY;VALUE=PERIOD:19971015T050000Z/PT8H30M,
19971015T160000Z/PT5H30M,19971015T223000Z/PT6H30M
URL:http://host2.com/pub/busy/jpublic-01.ifb COMMENT:This iCalendar
file contains busy time information for the next three months.
END:VFREEBUSY The following is an example of a "VFREEBUSY" calendar
component used to publish busy time information. BEGIN:VFREEBUSY
ORGANIZER:jsmith@host.com DTSTART:19980313T141711Z
DTEND:19980410T141711Z FREEBUSY:19980314T233000Z/19980315T003000Z
FREEBUSY:19980316T153000Z/19980316T163000Z
FREEBUSY:19980318T030000Z/19980318T040000Z
URL:http://www.host.com/calendar/busytime/jsmith.ifb END:VFREEBUSY
4.6.5 Time Zone Component Component Name: VTIMEZONE Purpose:
Provide a grouping of component properties that defines a time
zone. Formal Definition: A "VTIMEZONE" calendar component is
defined by the following notation: timezonec = "BEGIN" ":"
"VTIMEZONE" CRLF 2*( ; 'tzid' is required, but MUST NOT occur more
; than once tzid / ; 'last-mod' and 'tzurl' are optional, but MUST
NOT occur more than once Dawson & Stenerson Standards Track
[Page 60]
RFC 2445 iCalendar November 1998 last-mod / tzurl / ; one
of 'standardc' or 'daylightc' MUST occur ..; and each MAY occur
more than once. standardc / daylightc / ; the following is
optional, ; and MAY occur more than once x-prop ) "END" ":"
"VTIMEZONE" CRLF standardc = "BEGIN" ":" "STANDARD" CRLF tzprop
"END" ":" "STANDARD" CRLF daylightc = "BEGIN" ":" "DAYLIGHT" CRLF
tzprop "END" ":" "DAYLIGHT" CRLF tzprop = 3*( ; the following are
each REQUIRED, ; but MUST NOT occur more than once dtstart /
tzoffsetto / tzoffsetfrom / ; the following are optional, ; and MAY
occur more than once comment / rdate / rrule / tzname / x-prop )
Description: A time zone is unambiguously defined by the set of
time measurement rules determined by the governing body for a given
geographic area. These rules describe at a minimum the base offset
from UTC for the time zone, often referred to as the Standard Time
offset. Many locations adjust their Standard Time forward or
backward by one hour, in order to accommodate seasonal changes in
number of Dawson & Stenerson Standards Track [Page 61]
RFC 2445
iCalendar November 1998 daylight hours, often referred to as
Daylight Saving Time. Some locations adjust their time by a
fraction of an hour. Standard Time is also known as Winter Time.
Daylight Saving Time is also known as Advanced Time, Summer Time,
or Legal Time in certain countries. The following table shows the
changes in time zone rules in effect for New York City starting
from 1967. Each line represents a description or rule for a
particular observance. Effective Observance Rule Date (Date/Time)
Offset Abbreviation 1967-* last Sun in Oct, 02:00 -0500 EST
1967-1973 last Sun in Apr, 02:00 -0400 EDT 1974-1974 Jan 6, 02:00
-0400 EDT 1975-1975 Feb 23, 02:00 -0400 EDT 1976-1986 last Sun in
Apr, 02:00 -0400 EDT 1987-* first Sun in Apr, 02:00 -0400 EDT Note:
The specification of a global time zone registry is not addressed
by this document and is left for future study. However,
implementers may find the Olson time zone database [TZ] a useful
reference. It is an informal, public-domain collection of time zone
information, which is currently being maintained by volunteer
Internet participants, and is used in several operating systems.
This database contains current and historical time zone information
for a wide variety of locations around the globe; it provides a
time zone identifier for every unique time zone rule set in actual
use since 1970, with historical data going back to the introduction
of standard time. Interoperability between two calendaring and
scheduling applications, especially for recurring events, to-dos or
journal entries, is dependent on the ability to capture and convey
date and time information in an unambiguous format. The
specification of current time zone information is integral to this
behavior. If present, the "VTIMEZONE" calendar component defines
the set of Standard Time and Daylight Saving Time observances (or
rules) for a particular time zone for a given interval of time. The
"VTIMEZONE" calendar component cannot be nested within other
calendar components. Multiple "VTIMEZONE" calendar components can
exist in an iCalendar object. In this situation, each "VTIMEZONE"
MUST represent a unique Dawson & Stenerson Standards Track
[Page 62]
RFC 2445 iCalendar November 1998 time zone definition.
This is necessary for some classes of events, such as airline
flights, that start in one time zone and end in another. The
"VTIMEZONE" calendar component MUST be present if the iCalendar
object contains an RRULE that generates dates on both sides of a
time zone shift (e.g. both in Standard Time and Daylight Saving
Time) unless the iCalendar object intends to convey a floating time
(See the section "4.1.10.11 Time" for proper interpretation of
floating time). It can be present if the iCalendar object does not
contain such a RRULE. In addition, if a RRULE is present, there
MUST be valid time zone information for all recurrence instances.
The "VTIMEZONE" calendar component MUST include the "TZID" property
and at least one definition of a standard or daylight component.
The standard or daylight component MUST include the "DTSTART",
"TZOFFSETFROM" and "TZOFFSETTO" properties. An individual
"VTIMEZONE" calendar component MUST be specified for each unique
"TZID" parameter value specified in the iCalendar object. Each
"VTIMEZONE" calendar component consists of a collection of one or
more sub-components that describe the rule for a particular
observance (either a Standard Time or a Daylight Saving Time
observance). The "STANDARD" sub-component consists of a collection
of properties that describe Standard Time. The "DAYLIGHT"
sub-component consists of a collection of properties that describe
Daylight Saving Time. In general this collection of properties
consists of: - the first onset date-time for the observance - the
last onset date-time for the observance, if a last onset is known.
- the offset to be applied for the observance - a rule that
describes the day and time when the observance takes effect - an
optional name for the observance For a given time zone, there may
be multiple unique definitions of the observances over a period of
time. Each observance is described using either a "STANDARD" or
"DAYLIGHT" sub-component. The collection of these sub-components is
used to describe the time zone for a given period of time. The
offset to apply at any given time is found by locating the
observance that has the last onset date and time before the time in
question, and using the offset value from that Dawson &
Stenerson Standards Track [Page 63]
RFC 2445 iCalendar November
1998 observance. The top-level properties in a "VTIMEZONE" calendar
component are: The mandatory "TZID" property is a text value that
uniquely identifies the VTIMZONE calendar component within the
scope of an iCalendar object. The optional "LAST-MODIFIED" property
is a UTC value that specifies the date and time that this time zone
definition was last updated. The optional "TZURL" property is url
value that points to a published VTIMEZONE definition. TZURL SHOULD
refer to a resource that is accessible by anyone who might need to
interpret the object. This SHOULD NOT normally be a file: URL or
other URL that is not widely- accessible. The collection of
properties that are used to define the STANDARD and DAYLIGHT
sub-components include: The mandatory "DTSTART" property gives the
effective onset date and local time for the time zone sub-component
definition. "DTSTART" in this usage MUST be specified as a local
DATE-TIME value. The mandatory "TZOFFSETFROM" property gives the
UTC offset which is in use when the onset of this time zone
observance begins. "TZOFFSETFROM" is combined with "DTSTART" to
define the effective onset for the time zone sub-component
definition. For example, the following represents the time at which
the observance of Standard Time took effect in Fall 1967 for New
York City: DTSTART:19671029T020000 TZOFFSETFROM:-0400 The mandatory
"TZOFFSETTO " property gives the UTC offset for the time zone
sub-component (Standard Time or Daylight Saving Time) when this
observance is in use. The optional "TZNAME" property is the
customary name for the time zone. It may be specified multiple
times, to allow for specifying multiple language variants of the
time zone names. This could be used for displaying dates. If
specified, the onset for the observance defined by the time zone
sub-component is defined by either the "RRULE" or "RDATE" property.
If neither is specified, only one sub-component can be specified in
the "VTIMEZONE" calendar component and it is assumed that the
single Dawson & Stenerson Standards Track [Page 64]
RFC 2445
iCalendar November 1998 observance specified is always in effect.
The "RRULE" property defines the recurrence rule for the onset of
the observance defined by this time zone sub-component. Some
specific requirements for the usage of RRULE for this purpose
include: - If observance is known to have an effective end date,
the "UNTIL" recurrence rule parameter MUST be used to specify the
last valid onset of this observance (i.e., the UNTIL date-time will
be equal to the last instance generated by the recurrence pattern).
It MUST be specified in UTC time. - The "DTSTART" and the
"TZOFFSETTO" properties MUST be used when generating the onset
date-time values (instances) from the RRULE. Alternatively, the
"RDATE" property can be used to define the onset of the observance
by giving the individual onset date and times. "RDATE" in this
usage MUST be specified as a local DATE-TIME value in UTC time. The
optional "COMMENT" property is also allowed for descriptive
explanatory text. Example: The following are examples of the
"VTIMEZONE" calendar component: This is an example showing time
zone information for the Eastern United States using "RDATE"
property. Note that this is only suitable for a recurring event
that starts on or later than April 6, 1997 at 03:00:00 EDT (i.e.,
the earliest effective transition date and time) and ends no later
than April 7, 1998 02:00:00 EST (i.e., latest valid date and time
for EST in this scenario). For example, this can be used for a
recurring event that occurs every Friday, 8am-9:00 AM, starting
June 1, 1997, ending December 31, 1997. BEGIN:VTIMEZONE
TZID:US-Eastern LAST-MODIFIED:19870101T000000Z BEGIN:STANDARD
DTSTART:19971026T020000 RDATE:19971026T020000 TZOFFSETFROM:-0400
TZOFFSETTO:-0500 TZNAME:ES