RFC 2445
Internet Calendaring and Scheduling Core Object Specification (iCalendar)
4.3 Property Value Data Types The properties in an iCalendar object are strongly typed. The definition of each property restricts the value to be one of the value data types, or simply value types, defined in this section. The value type for a property will either be specified implicitly as the default value type or will be explicitly specified with the "VALUE"
parameter. If the value type of a property is one of the alternate valid types, then it MUST be explicitly specified with the "VALUE" parameter. 4.3.1 Binary Value Name: BINARY Purpose: This value type is used to identify properties that contain a character encoding of inline binary data. For example, an inline attachment of an object code might be included in an iCalendar object. Formal Definition: The value type is defined by the following notation: binary = *(4b-char) [b-end] ; A "BASE64" encoded character string, as defined by [RFC 2045]. b-end = (2b-char "==") / (3b-char "=") b-char = ALPHA / DIGIT / "+" / "/" Description: Property values with this value type MUST also include the inline encoding parameter sequence of ";ENCODING=BASE64". That is, all inline binary data MUST first be character encoded using the "BASE64" encoding method defined in [RFC 2045]. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. Example: The following is an abridged example of a "BASE64" encoded binary value data. ATTACH;VALUE=BINARY;ENCODING=BASE64:MIICajCCAdOgAwIBAgICBEUwDQY JKoZIhvcNAQEEBQAwdzELMAkGA1UEBhMCVVMxLDAqBgNVBAoTI05ldHNjYXBlI ENvbW11bmljYXRpb25zIENvcnBvcmF0aW9uMRwwGgYDVQQLExNJbmZv <...remainder of "BASE64" encoded binary data...> 4.3.2 Boolean Value Name: BOOLEAN Purpose: This value type is used to identify properties that contain either a "TRUE" or "FALSE" Boolean value. Formal Definition: The value type is defined by the following notation:
boolean = "TRUE" / "FALSE"
Description: These values are case insensitive text. No additional
content value encoding (i.e., BACKSLASH character encoding) is
defined for this value type.
Example: The following is an example of a hypothetical property that
has a BOOLEAN value type:
GIBBERISH:TRUE
4.3.3 Calendar User Address
Value Name: CAL-ADDRESS
Purpose: This value type is used to identify properties that contain
a calendar user address.
Formal Definition: The value type is as defined by the following
notation:
cal-address = uri
Description: The value is a URI as defined by [RFC 1738] or any other
IANA registered form for a URI. When used to address an Internet
email transport address for a calendar user, the value MUST be a
MAILTO URI, as defined by [RFC 1738]. No additional content value
encoding (i.e., BACKSLASH character encoding) is defined for this
value type.
Example:
ATTENDEE:MAILTO:jane_doe@host.com
4.3.4 Date
Value Name: DATE
Purpose: This value type is used to identify values that contain a
calendar date.
Formal Definition: The value type is defined by the following
notation:
date = date-value
date-value = date-fullyear date-month date-mday
date-fullyear = 4DIGIT
date-month = 2DIGIT ;01-12
date-mday = 2DIGIT ;01-28, 01-29, 01-30, 01-31
;based on month/year
Description: If the property permits, multiple "date" values are
specified as a COMMA character (US-ASCII decimal 44) separated list
of values. The format for the value type is expressed as the [ISO
8601] complete representation, basic format for a calendar date. The
textual format specifies a four-digit year, two-digit month, and
two-digit day of the month. There are no separator characters between
the year, month and day component text.
No additional content value encoding (i.e., BACKSLASH character
encoding) is defined for this value type.
Example: The following represents July 14, 1997:
19970714
4.3.5 Date-Time
Value Name: DATE-TIME
Purpose: This value type is used to identify values that specify a
precise calendar date and time of day.
Formal Definition: The value type is defined by the following
notation:
date-time = date "T" time ;As specified in the date and time
;value definitions
Description: If the property permits, multiple "date-time" values are
specified as a COMMA character (US-ASCII decimal 44) separated list
of values. No additional content value encoding (i.e., BACKSLASH
character encoding) is defined for this value type.
The "DATE-TIME" data type is used to identify values that contain a
precise calendar date and time of day. The format is based on the
[ISO 8601] complete representation, basic format for a calendar date
and time of day. The text format is a concatenation of the "date",
followed by the LATIN CAPITAL LETTER T character (US-ASCII decimal
84) time designator, followed by the "time" format.
The "DATE-TIME" data type expresses time values in three forms:
The form of date and time with UTC offset MUST NOT be used. For
example, the following is not valid for a date-time value:
DTSTART:19980119T230000-0800 ;Invalid time format
FORM #1: DATE WITH LOCAL TIME
The date with local time form is simply a date-time value that does
not contain the UTC designator nor does it reference a time zone. For
example, the following represents Janurary 18, 1998, at 11 PM:
DTSTART:19980118T230000
Date-time values of this type are said to be "floating" and are not
bound to any time zone in particular. They are used to represent the
same hour, minute, and second value regardless of which time zone is
currently being observed. For example, an event can be defined that
indicates that an individual will be busy from 11:00 AM to 1:00 PM
every day, no matter which time zone the person is in. In these
cases, a local time can be specified. The recipient of an iCalendar
object with a property value consisting of a local time, without any
relative time zone information, SHOULD interpret the value as being
fixed to whatever time zone the ATTENDEE is in at any given moment.
This means that two ATTENDEEs, in different time zones, receiving the
same event definition as a floating time, may be participating in the
event at different actual times. Floating time SHOULD only be used
where that is the reasonable behavior.
In most cases, a fixed time is desired. To properly communicate a
fixed time in a property value, either UTC time or local time with
time zone reference MUST be specified.
The use of local time in a DATE-TIME value without the TZID property
parameter is to be interpreted as floating time, regardless of the
existence of "VTIMEZONE" calendar components in the iCalendar object.
FORM #2: DATE WITH UTC TIME
The date with UTC time, or absolute time, is identified by a LATIN
CAPITAL LETTER Z suffix character (US-ASCII decimal 90), the UTC
designator, appended to the time value. For example, the following
represents January 19, 1998, at 0700 UTC:
DTSTART:19980119T070000Z
The TZID property parameter MUST NOT be applied to DATE-TIME
properties whose time values are specified in UTC.
FORM #3: DATE WITH LOCAL TIME AND TIME ZONE REFERENCE
The date and local time with reference to time zone information is
identified by the use the TZID property parameter to reference the
appropriate time zone definition. TZID is discussed in detail in the
section on Time Zone. For example, the following represents 2 AM in
New York on Janurary 19, 1998:
DTSTART;TZID=US-Eastern:19980119T020000
Example: The following represents July 14, 1997, at 1:30 PM in New
York City in each of the three time formats, using the "DTSTART"
property.
DTSTART:19970714T133000 ;Local time
DTSTART:19970714T173000Z ;UTC time
DTSTART;TZID=US-Eastern:19970714T133000 ;Local time and time
; zone reference
A time value MUST ONLY specify 60 seconds when specifying the
periodic "leap second" in the time value. For example:
COMPLETED:19970630T235960Z
4.3.6 Duration
Value Name: DURATION
Purpose: This value type is used to identify properties that contain
a duration of time.
Formal Definition: The value type is defined by the following
notation:
dur-value = (["+"] / "-") "P" (dur-date / dur-time / dur-week)
dur-date = dur-day [dur-time]
dur-time = "T" (dur-hour / dur-minute / dur-second)
dur-week = 1*DIGIT "W"
dur-hour = 1*DIGIT "H" [dur-minute]
dur-minute = 1*DIGIT "M" [dur-second]
dur-second = 1*DIGIT "S"
dur-day = 1*DIGIT "D"
Description: If the property permits, multiple "duration" values are
specified by a COMMA character (US-ASCII decimal 44) separated list
of values. The format is expressed as the [ISO 8601] basic format for
the duration of time. The format can represent durations in terms of
weeks, days, hours, minutes, and seconds.
No additional content value encoding (i.e., BACKSLASH character
encoding) are defined for this value type.
Example: A duration of 15 days, 5 hours and 20 seconds would be:
P15DT5H0M20S
A duration of 7 weeks would be:
P7W
4.3.7 Float
Value Name: FLOAT
Purpose: This value type is used to identify properties that contain
a real number value.
Formal Definition: The value type is defined by the following
notation:
float = (["+"] / "-") 1*DIGIT ["." 1*DIGIT]
Description: If the property permits, multiple "float" values are
specified by a COMMA character (US-ASCII decimal 44) separated list
of values.
No additional content value encoding (i.e., BACKSLASH character
encoding) is defined for this value type.
Example:
1000000.0000001
1.333
-3.14
4.3.8 Integer
Value Name:INTEGER
Purpose: This value type is used to identify properties that contain
a signed integer value.
Formal Definition: The value type is defined by the following
notation:
integer = (["+"] / "-") 1*DIGIT
Description: If the property permits, multiple "integer" values are
specified by a COMMA character (US-ASCII decimal 44) separated list
of values. The valid range for "integer" is -2147483648 to
2147483647. If the sign is not specified, then the value is assumed
to be positive.
No additional content value encoding (i.e., BACKSLASH character
encoding) is defined for this value type.
Example:
1234567890
-1234567890
+1234567890
432109876
4.3.9 Period of Time
Value Name: PERIOD
Purpose: This value type is used to identify values that contain a
precise period of time.
Formal Definition: The data type is defined by the following
notation:
period = period-explicit / period-start
period-explicit = date-time "/" date-time
; [ISO 8601] complete representation basic format for a period of
; time consisting of a start and end. The start MUST be before the
; end.
period-start = date-time "/" dur-value
; [ISO 8601] complete representation basic format for a period of
; time consisting of a start and positive duration of time.
Description: If the property permits, multiple "period" values are
specified by a COMMA character (US-ASCII decimal 44) separated list
of values. There are two forms of a period of time. First, a period
of time is identified by its start and its end. This format is
expressed as the [ISO 8601] complete representation, basic format for
"DATE-TIME" start of the period, followed by a SOLIDUS character
(US-ASCII decimal 47), followed by the "DATE-TIME" of the end of the
period. The start of the period MUST be before the end of the period.
Second, a period of time can also be defined by a start and a
positive duration of time. The format is expressed as the [ISO 8601]
complete representation, basic format for the "DATE-TIME" start of
the period, followed by a SOLIDUS character (US-ASCII decimal 47), followed by the [ISO 8601] basic format for "DURATION" of the period. Example: The period starting at 18:00:00 UTC, on January 1, 1997 and ending at 07:00:00 UTC on January 2, 1997 would be: 19970101T180000Z/19970102T070000Z The period start at 18:00:00 on January 1, 1997 and lasting 5 hours and 30 minutes would be: 19970101T180000Z/PT5H30M No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. 4.3.10 Recurrence Rule Value Name: RECUR Purpose: This value type is used to identify properties that contain a recurrence rule specification. Formal Definition: The value type is defined by the following notation: recur = "FREQ"=freq *( ; either UNTIL or COUNT may appear in a 'recur', ; but UNTIL and COUNT MUST NOT occur in the same 'recur' ( ";" "UNTIL" "=" enddate ) / ( ";" "COUNT" "=" 1*DIGIT ) / ; the rest of these keywords are optional, ; but MUST NOT occur more than once ( ";" "INTERVAL" "=" 1*DIGIT ) / ( ";" "BYSECOND" "=" byseclist ) / ( ";" "BYMINUTE" "=" byminlist ) / ( ";" "BYHOUR" "=" byhrlist ) / ( ";" "BYDAY" "=" bywdaylist ) / ( ";" "BYMONTHDAY" "=" bymodaylist ) / ( ";" "BYYEARDAY" "=" byyrdaylist ) / ( ";" "BYWEEKNO" "=" bywknolist ) / ( ";" "BYMONTH" "=" bymolist ) / ( ";" "BYSETPOS" "=" bysplist ) / ( ";" "WKST" "=" weekday ) /
( ";" x-name "=" text )
)
freq = "SECONDLY" / "MINUTELY" / "HOURLY" / "DAILY"
/ "WEEKLY" / "MONTHLY" / "YEARLY"
enddate = date
enddate =/ date-time ;An UTC value
byseclist = seconds / ( seconds *("," seconds) )
seconds = 1DIGIT / 2DIGIT ;0 to 59
byminlist = minutes / ( minutes *("," minutes) )
minutes = 1DIGIT / 2DIGIT ;0 to 59
byhrlist = hour / ( hour *("," hour) )
hour = 1DIGIT / 2DIGIT ;0 to 23
bywdaylist = weekdaynum / ( weekdaynum *("," weekdaynum) )
weekdaynum = [([plus] ordwk / minus ordwk)] weekday
plus = "+"
minus = "-"
ordwk = 1DIGIT / 2DIGIT ;1 to 53
weekday = "SU" / "MO" / "TU" / "WE" / "TH" / "FR" / "SA"
;Corresponding to SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY,
;FRIDAY, SATURDAY and SUNDAY days of the week.
bymodaylist = monthdaynum / ( monthdaynum *("," monthdaynum) )
monthdaynum = ([plus] ordmoday) / (minus ordmoday)
ordmoday = 1DIGIT / 2DIGIT ;1 to 31
byyrdaylist = yeardaynum / ( yeardaynum *("," yeardaynum) )
yeardaynum = ([plus] ordyrday) / (minus ordyrday)
ordyrday = 1DIGIT / 2DIGIT / 3DIGIT ;1 to 366
bywknolist = weeknum / ( weeknum *("," weeknum) )
weeknum = ([plus] ordwk) / (minus ordwk)
bymolist = monthnum / ( monthnum *("," monthnum) )
monthnum = 1DIGIT / 2DIGIT ;1 to 12
bysplist = setposday / ( setposday *("," setposday) )
setposday = yeardaynum
Description: If the property permits, multiple "recur" values are
specified by a COMMA character (US-ASCII decimal 44) separated list
of values. The value type is a structured value consisting of a list
of one or more recurrence grammar parts. Each rule part is defined by
a NAME=VALUE pair. The rule parts are separated from each other by
the SEMICOLON character (US-ASCII decimal 59). The rule parts are not
ordered in any particular sequence. Individual rule parts MUST only
be specified once.
The FREQ rule part identifies the type of recurrence rule. This rule
part MUST be specified in the recurrence rule. Valid values include
SECONDLY, to specify repeating events based on an interval of a
second or more; MINUTELY, to specify repeating events based on an
interval of a minute or more; HOURLY, to specify repeating events
based on an interval of an hour or more; DAILY, to specify repeating
events based on an interval of a day or more; WEEKLY, to specify
repeating events based on an interval of a week or more; MONTHLY, to
specify repeating events based on an interval of a month or more; and
YEARLY, to specify repeating events based on an interval of a year or
more.
The INTERVAL rule part contains a positive integer representing how
often the recurrence rule repeats. The default value is "1", meaning
every second for a SECONDLY rule, or every minute for a MINUTELY
rule, every hour for an HOURLY rule, every day for a DAILY rule,
every week for a WEEKLY rule, every month for a MONTHLY rule and
every year for a YEARLY rule.
The UNTIL rule part defines a date-time value which bounds the
recurrence rule in an inclusive manner. If the value specified by
UNTIL is synchronized with the specified recurrence, this date or
date-time becomes the last instance of the recurrence. If specified
as a date-time value, then it MUST be specified in an UTC time
format. If not present, and the COUNT rule part is also not present,
the RRULE is considered to repeat forever.
The COUNT rule part defines the number of occurrences at which to
range-bound the recurrence. The "DTSTART" property value, if
specified, counts as the first occurrence. The BYSECOND rule part specifies a COMMA character (US-ASCII decimal 44) separated list of seconds within a minute. Valid values are 0 to 59. The BYMINUTE rule part specifies a COMMA character (US-ASCII decimal 44) separated list of minutes within an hour. Valid values are 0 to 59. The BYHOUR rule part specifies a COMMA character (US- ASCII decimal 44) separated list of hours of the day. Valid values are 0 to 23. The BYDAY rule part specifies a COMMA character (US-ASCII decimal 44) separated list of days of the week; MO indicates Monday; TU indicates Tuesday; WE indicates Wednesday; TH indicates Thursday; FR indicates Friday; SA indicates Saturday; SU indicates Sunday. Each BYDAY value can also be preceded by a positive (+n) or negative (-n) integer. If present, this indicates the nth occurrence of the specific day within the MONTHLY or YEARLY RRULE. For example, within a MONTHLY rule, +1MO (or simply 1MO) represents the first Monday within the month, whereas -1MO represents the last Monday of the month. If an integer modifier is not present, it means all days of this type within the specified frequency. For example, within a MONTHLY rule, MO represents all Mondays within the month. The BYMONTHDAY rule part specifies a COMMA character (ASCII decimal 44) separated list of days of the month. Valid values are 1 to 31 or -31 to -1. For example, -10 represents the tenth to the last day of the month. The BYYEARDAY rule part specifies a COMMA character (US-ASCII decimal 44) separated list of days of the year. Valid values are 1 to 366 or -366 to -1. For example, -1 represents the last day of the year (December 31st) and -306 represents the 306th to the last day of the year (March 1st). The BYWEEKNO rule part specifies a COMMA character (US-ASCII decimal 44) separated list of ordinals specifying weeks of the year. Valid values are 1 to 53 or -53 to -1. This corresponds to weeks according to week numbering as defined in [ISO 8601]. A week is defined as a seven day period, starting on the day of the week defined to be the week start (see WKST). Week number one of the calendar year is the first week which contains at least four (4) days in that calendar year. This rule part is only valid for YEARLY rules. For example, 3 represents the third week of the year. Note: Assuming a Monday week start, week 53 can only occur when Thursday is January 1 or if it is a leap year and Wednesday is January 1.
The BYMONTH rule part specifies a COMMA character (US-ASCII decimal
44) separated list of months of the year. Valid values are 1 to 12.
The WKST rule part specifies the day on which the workweek starts.
Valid values are MO, TU, WE, TH, FR, SA and SU. This is significant
when a WEEKLY RRULE has an interval greater than 1, and a BYDAY rule
part is specified. This is also significant when in a YEARLY RRULE
when a BYWEEKNO rule part is specified. The default value is MO.
The BYSETPOS rule part specifies a COMMA character (US-ASCII decimal
44) separated list of values which corresponds to the nth occurrence
within the set of events specified by the rule. Valid values are 1 to
366 or -366 to -1. It MUST only be used in conjunction with another
BYxxx rule part. For example "the last work day of the month" could
be represented as:
RRULE:FREQ=MONTHLY;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=-1
Each BYSETPOS value can include a positive (+n) or negative (-n)
integer. If present, this indicates the nth occurrence of the
specific occurrence within the set of events specified by the rule.
If BYxxx rule part values are found which are beyond the available
scope (ie, BYMONTHDAY=30 in February), they are simply ignored.
Information, not contained in the rule, necessary to determine the
various recurrence instance start time and dates are derived from the
Start Time (DTSTART) entry attribute. For example,
"FREQ=YEARLY;BYMONTH=1" doesn't specify a specific day within the
month or a time. This information would be the same as what is
specified for DTSTART.
BYxxx rule parts modify the recurrence in some manner. BYxxx rule
parts for a period of time which is the same or greater than the
frequency generally reduce or limit the number of occurrences of the
recurrence generated. For example, "FREQ=DAILY;BYMONTH=1" reduces the
number of recurrence instances from all days (if BYMONTH tag is not
present) to all days in January. BYxxx rule parts for a period of
time less than the frequency generally increase or expand the number
of occurrences of the recurrence. For example,
"FREQ=YEARLY;BYMONTH=1,2" increases the number of days within the
yearly recurrence set from 1 (if BYMONTH tag is not present) to 2.
If multiple BYxxx rule parts are specified, then after evaluating the
specified FREQ and INTERVAL rule parts, the BYxxx rule parts are
applied to the current set of evaluated occurrences in the following
order: BYMONTH, BYWEEKNO, BYYEARDAY, BYMONTHDAY, BYDAY, BYHOUR,
BYMINUTE, BYSECOND and BYSETPOS; then COUNT and UNTIL are evaluated.
Here is an example of evaluating multiple BYxxx rule parts.
DTSTART;TZID=US-Eastern:19970105T083000
RRULE:FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9;
BYMINUTE=30
First, the "INTERVAL=2" would be applied to "FREQ=YEARLY" to arrive
at "every other year". Then, "BYMONTH=1" would be applied to arrive
at "every January, every other year". Then, "BYDAY=SU" would be
applied to arrive at "every Sunday in January, every other year".
Then, "BYHOUR=8,9" would be applied to arrive at "every Sunday in
January at 8 AM and 9 AM, every other year". Then, "BYMINUTE=30"
would be applied to arrive at "every Sunday in January at 8:30 AM and
9:30 AM, every other year". Then, lacking information from RRULE, the
second is derived from DTSTART, to end up in "every Sunday in January
at 8:30:00 AM and 9:30:00 AM, every other year". Similarly, if the
BYMINUTE, BYHOUR, BYDAY, BYMONTHDAY or BYMONTH rule part were
missing, the appropriate minute, hour, day or month would have been
retrieved from the "DTSTART" property.
No additional content value encoding (i.e., BACKSLASH character
encoding) is defined for this value type.
Example: The following is a rule which specifies 10 meetings which
occur every other day:
FREQ=DAILY;COUNT=10;INTERVAL=2
There are other examples specified in the "RRULE" specification.
4.3.11 Text
Value Name: TEXT
Purpose This value type is used to identify values that contain human
readable text.
Formal Definition: The character sets supported by this revision of
iCalendar are UTF-8 and US ASCII thereof. The applicability to other
character sets is for future work. The value type is defined by the
following notation.
text = *(TSAFE-CHAR / ":" / DQUOTE / ESCAPED-CHAR)
; Folded according to description above
ESCAPED-CHAR = "\\" / "\;" / "\," / "\N" / "\n")
; \\ encodes \, \N or \n encodes newline
; \; encodes ;, \, encodes ,
TSAFE-CHAR = %x20-21 / %x23-2B / %x2D-39 / %x3C-5B
%x5D-7E / NON-US-ASCII
; Any character except CTLs not needed by the current
; character set, DQUOTE, ";", ":", "\", ","
Note: Certain other character sets may require modification of the
above definitions, but this is beyond the scope of this document.
Description: If the property permits, multiple "text" values are
specified by a COMMA character (US-ASCII decimal 44) separated list
of values.
The language in which the text is represented can be controlled by
the "LANGUAGE" property parameter.
An intentional formatted text line break MUST only be included in a
"TEXT" property value by representing the line break with the
character sequence of BACKSLASH (US-ASCII decimal 92), followed by a
LATIN SMALL LETTER N (US-ASCII decimal 110) or a LATIN CAPITAL LETTER
N (US-ASCII decimal 78), that is "\n" or "\N".
The "TEXT" property values may also contain special characters that
are used to signify delimiters, such as a COMMA character for lists
of values or a SEMICOLON character for structured values. In order to
support the inclusion of these special characters in "TEXT" property
values, they MUST be escaped with a BACKSLASH character. A BACKSLASH
character (US-ASCII decimal 92) in a "TEXT" property value MUST be
escaped with another BACKSLASH character. A COMMA character in a
"TEXT" property value MUST be escaped with a BACKSLASH character
(US-ASCII decimal 92). A SEMICOLON character in a "TEXT" property
value MUST be escaped with a BACKSLASH character (US-ASCII decimal
92). However, a COLON character in a "TEXT" property value SHALL NOT
be escaped with a BACKSLASH character.Example: A multiple line value
of:
Project XYZ Final Review
Conference Room - 3B
Come Prepared.
would be represented as:
Project XYZ Final Review\nConference Room - 3B\nCome Prepared.
4.3.12 Time Value Name: TIME Purpose: This value type is used to identify values that contain a time of day. Formal Definition: The data type is defined by the following notation: time = time-hour time-minute time-second [time-utc] time-hour = 2DIGIT ;00-23 time-minute = 2DIGIT ;00-59 time-second = 2DIGIT ;00-60 ;The "60" value is used to account for "leap" seconds. time-utc = "Z" Description: If the property permits, multiple "time" values are specified by a COMMA character (US-ASCII decimal 44) separated list of values. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. The "TIME" data type is used to identify values that contain a time of day. The format is based on the [ISO 8601] complete representation, basic format for a time of day. The text format consists of a two-digit 24-hour of the day (i.e., values 0-23), two- digit minute in the hour (i.e., values 0-59), and two-digit seconds in the minute (i.e., values 0-60). The seconds value of 60 MUST only to be used to account for "leap" seconds. Fractions of a second are not supported by this format. In parallel to the "DATE-TIME" definition above, the "TIME" data type expresses time values in three forms: The form of time with UTC offset MUST NOT be used. For example, the following is NOT VALID for a time value: 230000-0800 ;Invalid time format FORM #1 LOCAL TIME The local time form is simply a time value that does not contain the UTC designator nor does it reference a time zone. For example, 11:00 PM: 230000
Time values of this type are said to be "floating" and are not bound
to any time zone in particular. They are used to represent the same
hour, minute, and second value regardless of which time zone is
currently being observed. For example, an event can be defined that
indicates that an individual will be busy from 11:00 AM to 1:00 PM
every day, no matter which time zone the person is in. In these
cases, a local time can be specified. The recipient of an iCalendar
object with a property value consisting of a local time, without any
relative time zone information, SHOULD interpret the value as being
fixed to whatever time zone the ATTENDEE is in at any given moment.
This means that two ATTENDEEs may participate in the same event at
different UTC times; floating time SHOULD only be used where that is
reasonable behavior.
In most cases, a fixed time is desired. To properly communicate a
fixed time in a property value, either UTC time or local time with
time zone reference MUST be specified.
The use of local time in a TIME value without the TZID property
parameter is to be interpreted as a local time value, regardless of
the existence of "VTIMEZONE" calendar components in the iCalendar
object.
FORM #2: UTC TIME
UTC time, or absolute time, is identified by a LATIN CAPITAL LETTER Z
suffix character (US-ASCII decimal 90), the UTC designator, appended
to the time value. For example, the following represents 07:00 AM
UTC:
070000Z
The TZID property parameter MUST NOT be applied to TIME properties
whose time values are specified in UTC.
FORM #3: LOCAL TIME AND TIME ZONE REFERENCE
The local time with reference to time zone information form is
identified by the use the TZID property parameter to reference the
appropriate time zone definition. TZID is discussed in detail in the
section on Time Zone.
Example: The following represents 8:30 AM in New York in Winter, five
hours behind UTC, in each of the three formats using the "X-
TIMEOFDAY" non-standard property:
X-TIMEOFDAY:083000
X-TIMEOFDAY:133000Z
X-TIMEOFDAY;TZID=US-Eastern:083000
4.3.13 URI
Value Name: URI
Purpose: This value type is used to identify values that contain a
uniform resource identifier (URI) type of reference to the property
value.
Formal Definition: The data type is defined by the following
notation:
uri = <As defined by any IETF RFC>
Description: This data type might be used to reference binary
information, for values that are large, or otherwise undesirable to
include directly in the iCalendar object.
The URI value formats in RFC 1738, RFC 2111 and any other IETF
registered value format can be specified.
Any IANA registered URI format can be used. These include, but are
not limited to, those defined in RFC 1738 and RFC 2111.
When a property parameter value is a URI value type, the URI MUST be
specified as a quoted-string value.
No additional content value encoding (i.e., BACKSLASH character
encoding) is defined for this value type.
Example: The following is a URI for a network file:
http://host1.com/my-report.txt
4.3.14 UTC Offset
Value Name: UTC-OFFSET
Purpose: This value type is used to identify properties that contain
an offset from UTC to local time.
Formal Definition: The data type is defined by the following
notation:
utc-offset = time-numzone ;As defined above in time data type
time-numzone = ("+" / "-") time-hour time-minute [time-
second]
Description: The PLUS SIGN character MUST be specified for positive
UTC offsets (i.e., ahead of UTC). The value of "-0000" and "-000000"
are not allowed. The time-second, if present, may not be 60; if
absent, it defaults to zero.
No additional content value encoding (i.e., BACKSLASH character
encoding) is defined for this value type.
Example: The following UTC offsets are given for standard time for
New York (five hours behind UTC) and Geneva (one hour ahead of UTC):
-0500
+0100
4.4 iCalendar Object
The Calendaring and Scheduling Core Object is a collection of
calendaring and scheduling information. Typically, this information
will consist of a single iCalendar object. However, multiple
iCalendar objects can be sequentially grouped together. The first
line and last line of the iCalendar object MUST contain a pair of
iCalendar object delimiter strings. The syntax for an iCalendar
object is as follows:
icalobject = 1*("BEGIN" ":" "VCALENDAR" CRLF
icalbody
"END" ":" "VCALENDAR" CRLF)
The following is a simple example of an iCalendar object:
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN
BEGIN:VEVENT
DTSTART:19970714T170000Z
DTEND:19970715T035959Z
SUMMARY:Bastille Day Party
END:VEVENT
END:VCALENDAR
4.5 Property A property is the definition of an individual attribute describing a calendar or a calendar component. A property takes the form defined by the "contentline" notation defined in section 4.1.1. The following is an example of a property: DTSTART:19960415T133000Z This memo imposes no ordering of properties within an iCalendar object. Property names, parameter names and enumerated parameter values are case insensitive. For example, the property name "DUE" is the same as "due" and "Due", DTSTART;TZID=US-Eastern:19980714T120000 is the same as DtStart;TzID=US-Eastern:19980714T120000. 4.6 Calendar Components The body of the iCalendar object consists of a sequence of calendar properties and one or more calendar components. The calendar properties are attributes that apply to the calendar as a whole. The calendar components are collections of properties that express a particular calendar semantic. For example, the calendar component can specify an event, a to-do, a journal entry, time zone information, or free/busy time information, or an alarm. The body of the iCalendar object is defined by the following notation: icalbody = calprops component calprops = 2*( ; 'prodid' and 'version' are both REQUIRED, ; but MUST NOT occur more than once prodid /version / ; 'calscale' and 'method' are optional, ; but MUST NOT occur more than once calscale / method / x-prop
)
component = 1*(eventc / todoc / journalc / freebusyc /
/ timezonec / iana-comp / x-comp)
iana-comp = "BEGIN" ":" iana-token CRLF
1*contentline
"END" ":" iana-token CRLF
x-comp = "BEGIN" ":" x-name CRLF
1*contentline
"END" ":" x-name CRLF
An iCalendar object MUST include the "PRODID" and "VERSION" calendar
properties. In addition, it MUST include at least one calendar
component. Special forms of iCalendar objects are possible to publish
just busy time (i.e., only a "VFREEBUSY" calendar component) or time
zone (i.e., only a "VTIMEZONE" calendar component) information. In
addition, a complex iCalendar object is possible that is used to
capture a complete snapshot of the contents of a calendar (e.g.,
composite of many different calendar components). More commonly, an
iCalendar object will consist of just a single "VEVENT", "VTODO" or
"VJOURNAL" calendar component.
4.6.1 Event Component
Component Name: "VEVENT"
Purpose: Provide a grouping of component properties that describe an
event.
Format Definition: A "VEVENT" calendar component is defined by the
following notation:
eventc = "BEGIN" ":" "VEVENT" CRLF
eventprop *alarmc
"END" ":" "VEVENT" CRLF
eventprop = *(
; the following are optional,
; but MUST NOT occur more than once
class / created / description / dtstart / geo /
last-mod / location / organizer / priority /
dtstamp / seq / status / summary / transp /
uid / url / recurid /
; either 'dtend' or 'duration' may appear in
; a 'eventprop', but 'dtend' and 'duration'
; MUST NOT occur in the same 'eventprop'
dtend / duration /
; the following are optional,
; and MAY occur more than once
attach / attendee / categories / comment /
contact / exdate / exrule / rstatus / related /
resources / rdate / rrule / x-prop
)
Description: A "VEVENT" calendar component is a grouping of component
properties, and possibly including "VALARM" calendar components, that
represents a scheduled amount of time on a calendar. For example, it
can be an activity; such as a one-hour long, department meeting from
8:00 AM to 9:00 AM, tomorrow. Generally, an event will take up time
on an individual calendar. Hence, the event will appear as an opaque
interval in a search for busy time. Alternately, the event can have
its Time Transparency set to "TRANSPARENT" in order to prevent
blocking of the event in searches for busy time.
The "VEVENT" is also the calendar component used to specify an
anniversary or daily reminder within a calendar. These events have a
DATE value type for the "DTSTART" property instead of the default
data type of DATE-TIME. If such a "VEVENT" has a "DTEND" property, it
MUST be specified as a DATE value also. The anniversary type of
"VEVENT" can span more than one date (i.e, "DTEND" property value is
set to a calendar date after the "DTSTART" property value).
The "DTSTART" property for a "VEVENT" specifies the inclusive start
of the event. For recurring events, it also specifies the very first
instance in the recurrence set. The "DTEND" property for a "VEVENT"
calendar component specifies the non-inclusive end of the event. For
cases where a "VEVENT" calendar component specifies a "DTSTART"
property with a DATE data type but no "DTEND" property, the events
non-inclusive end is the end of the calendar date specified by the
"DTSTART" property. For cases where a "VEVENT" calendar component
specifies a "DTSTART" property with a DATE-TIME data type but no
"DTEND" property, the event ends on the same calendar date and time
of day specified by the "DTSTART" property.
The "VEVENT" calendar component cannot be nested within another
calendar component. However, "VEVENT" calendar components can be
related to each other or to a "VTODO" or to a "VJOURNAL" calendar
component with the "RELATED-TO" property.
Example: The following is an example of the "VEVENT" calendar
component used to represent a meeting that will also be opaque to
searches for busy time:
BEGIN:VEVENT
UID:19970901T130000Z-123401@host.com
DTSTAMP:19970901T1300Z
DTSTART:19970903T163000Z
DTEND:19970903T190000Z
SUMMARY:Annual Employee Review
CLASS:PRIVATE
CATEGORIES:BUSINESS,HUMAN RESOURCES
END:VEVENT
The following is an example of the "VEVENT" calendar component used
to represent a reminder that will not be opaque, but rather
transparent, to searches for busy time:
BEGIN:VEVENT
UID:19970901T130000Z-123402@host.com
DTSTAMP:19970901T1300Z
DTSTART:19970401T163000Z
DTEND:19970402T010000Z
SUMMARY:Laurel is in sensitivity awareness class.
CLASS:PUBLIC
CATEGORIES:BUSINESS,HUMAN RESOURCES
TRANSP:TRANSPARENT
END:VEVENT
The following is an example of the "VEVENT" calendar component used
to represent an anniversary that will occur annually. Since it takes
up no time, it will not appear as opaque in a search for busy time;
no matter what the value of the "TRANSP" property indicates:
BEGIN:VEVENT
UID:19970901T130000Z-123403@host.com
DTSTAMP:19970901T1300Z
DTSTART:19971102
SUMMARY:Our Blissful Anniversary
CLASS:CONFIDENTIAL
CATEGORIES:ANNIVERSARY,PERSONAL,SPECIAL OCCASION
RRULE:FREQ=YEARLY
END:VEVENT
4.6.2 To-do Component Component Name: VTODO Purpose: Provide a grouping of calendar properties that describe a to-do. Formal Definition: A "VTODO" calendar component is defined by the following notation: todoc = "BEGIN" ":" "VTODO" CRLF todoprop *alarmc "END" ":" "VTODO" CRLF todoprop = *( ; the following are optional, ; but MUST NOT occur more than once class / completed / created / description / dtstamp / dtstart / geo / last-mod / location / organizer / percent / priority / recurid / seq / status / summary / uid / url / ; either 'due' or 'duration' may appear in ; a 'todoprop', but 'due' and 'duration' ; MUST NOT occur in the same 'todoprop' due / duration / ; the following are optional, ; and MAY occur more than once attach / attendee / categories / comment / contact / exdate / exrule / rstatus / related / resources / rdate / rrule / x-prop ) Description: A "VTODO" calendar component is a grouping of component properties and possibly "VALARM" calendar components that represent an action-item or assignment. For example, it can be used to represent an item of work assigned to an individual; such as "turn in travel expense today". The "VTODO" calendar component cannot be nested within another calendar component. However, "VTODO" calendar components can be related to each other or to a "VTODO" or to a "VJOURNAL" calendar component with the "RELATED-TO" property.
A "VTODO" calendar component without the "DTSTART" and "DUE" (or
"DURATION") properties specifies a to-do that will be associated with
each successive calendar date, until it is completed.
Example: The following is an example of a "VTODO" calendar component:
BEGIN:VTODO
UID:19970901T130000Z-123404@host.com
DTSTAMP:19970901T1300Z
DTSTART:19970415T133000Z
DUE:19970416T045959Z
SUMMARY:1996 Income Tax Preparation
CLASS:CONFIDENTIAL
CATEGORIES:FAMILY,FINANCE
PRIORITY:1
STATUS:NEEDS-ACTION
END:VTODO
4.6.3 Journal Component
Component Name: VJOURNAL
Purpose: Provide a grouping of component properties that describe a
journal entry.
Formal Definition: A "VJOURNAL" calendar component is defined by the
following notation:
journalc = "BEGIN" ":" "VJOURNAL" CRLF
jourprop
"END" ":" "VJOURNAL" CRLF
jourprop = *(
; the following are optional,
; but MUST NOT occur more than once
class / created / description / dtstart / dtstamp /
last-mod / organizer / recurid / seq / status /
summary / uid / url /
; the following are optional,
; and MAY occur more than once
attach / attendee / categories / comment /
contact / exdate / exrule / related / rdate /
rrule / rstatus / x-prop
)
Description: A "VJOURNAL" calendar component is a grouping of
component properties that represent one or more descriptive text
notes associated with a particular calendar date. The "DTSTART"
property is used to specify the calendar date that the journal entry
is associated with. Generally, it will have a DATE value data type,
but it can also be used to specify a DATE-TIME value data type.
Examples of a journal entry include a daily record of a legislative
body or a journal entry of individual telephone contacts for the day
or an ordered list of accomplishments for the day. The "VJOURNAL"
calendar component can also be used to associate a document with a
calendar date.
The "VJOURNAL" calendar component does not take up time on a
calendar. Hence, it does not play a role in free or busy time
searches - - it is as though it has a time transparency value of
TRANSPARENT. It is transparent to any such searches.
The "VJOURNAL" calendar component cannot be nested within another
calendar component. However, "VJOURNAL" calendar components can be
related to each other or to a "VEVENT" or to a "VTODO" calendar
component, with the "RELATED-TO" property.
Example: The following is an example of the "VJOURNAL" calendar
component:
BEGIN:VJOURNAL
UID:19970901T130000Z-123405@host.com
DTSTAMP:19970901T1300Z
DTSTART;VALUE=DATE:19970317
SUMMARY:Staff meeting minutes
DESCRIPTION:1. Staff meeting: Participants include Joe\, Lisa
and Bob. Aurora project plans were reviewed. There is currently
no budget reserves for this project. Lisa will escalate to
management. Next meeting on Tuesday.\n
2. Telephone Conference: ABC Corp. sales representative called
to discuss new printer. Promised to get us a demo by Friday.\n
3. Henry Miller (Handsoff Insurance): Car was totaled by tree.
Is looking into a loaner car. 654-2323 (tel).
END:VJOURNAL
4.6.4 Free/Busy Component Component Name: VFREEBUSY Purpose: Provide a grouping of component properties that describe either a request for free/busy time, describe a response to a request for free/busy time or describe a published set of busy time. Formal Definition: A "VFREEBUSY" calendar component is defined by the following notation: freebusyc = "BEGIN" ":" "VFREEBUSY" CRLF fbprop "END" ":" "VFREEBUSY" CRLF fbprop = *( ; the following are optional, ; but MUST NOT occur more than once contact / dtstart / dtend / duration / dtstamp / organizer / uid / url / ; the following are optional, ; and MAY occur more than once attendee / comment / freebusy / rstatus / x-prop ) Description: A "VFREEBUSY" calendar component is a grouping of component properties that represents either a request for, a reply to a request for free or busy time information or a published set of busy time information. When used to request free/busy time information, the "ATTENDEE" property specifies the calendar users whose free/busy time is being requested; the "ORGANIZER" property specifies the calendar user who is requesting the free/busy time; the "DTSTART" and "DTEND" properties specify the window of time for which the free/busy time is being requested; the "UID" and "DTSTAMP" properties are specified to assist in proper sequencing of multiple free/busy time requests. When used to reply to a request for free/busy time, the "ATTENDEE" property specifies the calendar user responding to the free/busy time request; the "ORGANIZER" property specifies the calendar user that originally requested the free/busy time; the "FREEBUSY" property specifies the free/busy time information (if it exists); and the
"UID" and "DTSTAMP" properties are specified to assist in proper
sequencing of multiple free/busy time replies.
When used to publish busy time, the "ORGANIZER" property specifies
the calendar user associated with the published busy time; the
"DTSTART" and "DTEND" properties specify an inclusive time window
that surrounds the busy time information; the "FREEBUSY" property
specifies the published busy time information; and the "DTSTAMP"
property specifies the date/time that iCalendar object was created.
The "VFREEBUSY" calendar component cannot be nested within another
calendar component. Multiple "VFREEBUSY" calendar components can be
specified within an iCalendar object. This permits the grouping of
Free/Busy information into logical collections, such as monthly
groups of busy time information.
The "VFREEBUSY" calendar component is intended for use in iCalendar
object methods involving requests for free time, requests for busy
time, requests for both free and busy, and the associated replies.
Free/Busy information is represented with the "FREEBUSY" property.
This property provides a terse representation of time periods. One or
more "FREEBUSY" properties can be specified in the "VFREEBUSY"
calendar component.
When present in a "VFREEBUSY" calendar component, the "DTSTART" and
"DTEND" properties SHOULD be specified prior to any "FREEBUSY"
properties. In a free time request, these properties can be used in
combination with the "DURATION" property to represent a request for a
duration of free time within a specified window of time.
The recurrence properties ("RRULE", "EXRULE", "RDATE", "EXDATE") are
not permitted within a "VFREEBUSY" calendar component. Any recurring
events are resolved into their individual busy time periods using the
"FREEBUSY" property.
Example: The following is an example of a "VFREEBUSY" calendar
component used to request free or busy time information:
BEGIN:VFREEBUSY
ORGANIZER:MAILTO:jane_doe@host1.com
ATTENDEE:MAILTO:john_public@host2.com
DTSTART:19971015T050000Z
DTEND:19971016T050000Z
DTSTAMP:19970901T083000Z
END:VFREEBUSY
The following is an example of a "VFREEBUSY" calendar component used
to reply to the request with busy time information:
BEGIN:VFREEBUSY
ORGANIZER:MAILTO:jane_doe@host1.com
ATTENDEE:MAILTO:john_public@host2.com
DTSTAMP:19970901T100000Z
FREEBUSY;VALUE=PERIOD:19971015T050000Z/PT8H30M,
19971015T160000Z/PT5H30M,19971015T223000Z/PT6H30M
URL:http://host2.com/pub/busy/jpublic-01.ifb
COMMENT:This iCalendar file contains busy time information for
the next three months.
END:VFREEBUSY
The following is an example of a "VFREEBUSY" calendar component used
to publish busy time information.
BEGIN:VFREEBUSY
ORGANIZER:jsmith@host.com
DTSTART:19980313T141711Z
DTEND:19980410T141711Z
FREEBUSY:19980314T233000Z/19980315T003000Z
FREEBUSY:19980316T153000Z/19980316T163000Z
FREEBUSY:19980318T030000Z/19980318T040000Z
URL:http://www.host.com/calendar/busytime/jsmith.ifb
END:VFREEBUSY
4.6.5 Time Zone Component
Component Name: VTIMEZONE
Purpose: Provide a grouping of component properties that defines a
time zone.
Formal Definition: A "VTIMEZONE" calendar component is defined by the
following notation:
timezonec = "BEGIN" ":" "VTIMEZONE" CRLF
2*(
; 'tzid' is required, but MUST NOT occur more
; than once
tzid /
; 'last-mod' and 'tzurl' are optional,
but MUST NOT occur more than once
last-mod / tzurl /
; one of 'standardc' or 'daylightc' MUST occur
..; and each MAY occur more than once.
standardc / daylightc /
; the following is optional,
; and MAY occur more than once
x-prop
)
"END" ":" "VTIMEZONE" CRLF
standardc = "BEGIN" ":" "STANDARD" CRLF
tzprop
"END" ":" "STANDARD" CRLF
daylightc = "BEGIN" ":" "DAYLIGHT" CRLF
tzprop
"END" ":" "DAYLIGHT" CRLF
tzprop = 3*(
; the following are each REQUIRED,
; but MUST NOT occur more than once
dtstart / tzoffsetto / tzoffsetfrom /
; the following are optional,
; and MAY occur more than once
comment / rdate / rrule / tzname / x-prop
)
Description: A time zone is unambiguously defined by the set of time
measurement rules determined by the governing body for a given
geographic area. These rules describe at a minimum the base offset
from UTC for the time zone, often referred to as the Standard Time
offset. Many locations adjust their Standard Time forward or backward
by one hour, in order to accommodate seasonal changes in number of
daylight hours, often referred to as Daylight Saving Time. Some
locations adjust their time by a fraction of an hour. Standard Time
is also known as Winter Time. Daylight Saving Time is also known as
Advanced Time, Summer Time, or Legal Time in certain countries. The
following table shows the changes in time zone rules in effect for
New York City starting from 1967. Each line represents a description
or rule for a particular observance.
Effective Observance Rule
Date (Date/Time) Offset Abbreviation
1967-* last Sun in Oct, 02:00 -0500 EST
1967-1973 last Sun in Apr, 02:00 -0400 EDT
1974-1974 Jan 6, 02:00 -0400 EDT
1975-1975 Feb 23, 02:00 -0400 EDT
1976-1986 last Sun in Apr, 02:00 -0400 EDT
1987-* first Sun in Apr, 02:00 -0400 EDT
Note: The specification of a global time zone registry is not
addressed by this document and is left for future study.
However, implementers may find the Olson time zone database [TZ]
a useful reference. It is an informal, public-domain collection
of time zone information, which is currently being maintained by
volunteer Internet participants, and is used in several
operating systems. This database contains current and historical
time zone information for a wide variety of locations around the
globe; it provides a time zone identifier for every unique time
zone rule set in actual use since 1970, with historical data
going back to the introduction of standard time.
Interoperability between two calendaring and scheduling applications,
especially for recurring events, to-dos or journal entries, is
dependent on the ability to capture and convey date and time
information in an unambiguous format. The specification of current
time zone information is integral to this behavior.
If present, the "VTIMEZONE" calendar component defines the set of
Standard Time and Daylight Saving Time observances (or rules) for a
particular time zone for a given interval of time. The "VTIMEZONE"
calendar component cannot be nested within other calendar components.
Multiple "VTIMEZONE" calendar components can exist in an iCalendar
object. In this situation, each "VTIMEZONE" MUST represent a unique
time zone definition. This is necessary for some classes of events,
such as airline flights, that start in one time zone and end in
another.
The "VTIMEZONE" calendar component MUST be present if the iCalendar
object contains an RRULE that generates dates on both sides of a time
zone shift (e.g. both in Standard Time and Daylight Saving Time)
unless the iCalendar object intends to convey a floating time (See
the section "4.1.10.11 Time" for proper interpretation of floating
time). It can be present if the iCalendar object does not contain
such a RRULE. In addition, if a RRULE is present, there MUST be valid
time zone information for all recurrence instances.
The "VTIMEZONE" calendar component MUST include the "TZID" property
and at least one definition of a standard or daylight component. The
standard or daylight component MUST include the "DTSTART",
"TZOFFSETFROM" and "TZOFFSETTO" properties.
An individual "VTIMEZONE" calendar component MUST be specified for
each unique "TZID" parameter value specified in the iCalendar object.
Each "VTIMEZONE" calendar component consists of a collection of one
or more sub-components that describe the rule for a particular
observance (either a Standard Time or a Daylight Saving Time
observance). The "STANDARD" sub-component consists of a collection of
properties that describe Standard Time. The "DAYLIGHT" sub-component
consists of a collection of properties that describe Daylight Saving
Time. In general this collection of properties consists of:
- the first onset date-time for the observance
- the last onset date-time for the observance, if a last onset
is known.
- the offset to be applied for the observance
- a rule that describes the day and time when the observance
takes effect
- an optional name for the observance
For a given time zone, there may be multiple unique definitions of
the observances over a period of time. Each observance is described
using either a "STANDARD" or "DAYLIGHT" sub-component. The collection
of these sub-components is used to describe the time zone for a given
period of time. The offset to apply at any given time is found by
locating the observance that has the last onset date and time before
the time in question, and using the offset value from that
observance.
The top-level properties in a "VTIMEZONE" calendar component are:
The mandatory "TZID" property is a text value that uniquely
identifies the VTIMZONE calendar component within the scope of an
iCalendar object.
The optional "LAST-MODIFIED" property is a UTC value that specifies
the date and time that this time zone definition was last updated.
The optional "TZURL" property is url value that points to a published
VTIMEZONE definition. TZURL SHOULD refer to a resource that is
accessible by anyone who might need to interpret the object. This
SHOULD NOT normally be a file: URL or other URL that is not widely-
accessible.
The collection of properties that are used to define the STANDARD and
DAYLIGHT sub-components include:
The mandatory "DTSTART" property gives the effective onset date and
local time for the time zone sub-component definition. "DTSTART" in
this usage MUST be specified as a local DATE-TIME value.
The mandatory "TZOFFSETFROM" property gives the UTC offset which is
in use when the onset of this time zone observance begins.
"TZOFFSETFROM" is combined with "DTSTART" to define the effective
onset for the time zone sub-component definition. For example, the
following represents the time at which the observance of Standard
Time took effect in Fall 1967 for New York City:
DTSTART:19671029T020000
TZOFFSETFROM:-0400
The mandatory "TZOFFSETTO " property gives the UTC offset for the
time zone sub-component (Standard Time or Daylight Saving Time) when
this observance is in use.
The optional "TZNAME" property is the customary name for the time
zone. It may be specified multiple times, to allow for specifying
multiple language variants of the time zone names. This could be used
for displaying dates.
If specified, the onset for the observance defined by the time zone
sub-component is defined by either the "RRULE" or "RDATE" property.
If neither is specified, only one sub-component can be specified in
the "VTIMEZONE" calendar component and it is assumed that the single
observance specified is always in effect.
The "RRULE" property defines the recurrence rule for the onset of the
observance defined by this time zone sub-component. Some specific
requirements for the usage of RRULE for this purpose include:
- If observance is known to have an effective end date, the
"UNTIL" recurrence rule parameter MUST be used to specify the
last valid onset of this observance (i.e., the UNTIL date-time
will be equal to the last instance generated by the recurrence
pattern). It MUST be specified in UTC time.
- The "DTSTART" and the "TZOFFSETTO" properties MUST be used
when generating the onset date-time values (instances) from the
RRULE.
Alternatively, the "RDATE" property can be used to define the onset
of the observance by giving the individual onset date and times.
"RDATE" in this usage MUST be specified as a local DATE-TIME value in
UTC time.
The optional "COMMENT" property is also allowed for descriptive
explanatory text.
Example: The following are examples of the "VTIMEZONE" calendar
component:
This is an example showing time zone information for the Eastern
United States using "RDATE" property. Note that this is only suitable
for a recurring event that starts on or later than April 6, 1997 at
03:00:00 EDT (i.e., the earliest effective transition date and time)
and ends no later than April 7, 1998 02:00:00 EST (i.e., latest valid
date and time for EST in this scenario). For example, this can be
used for a recurring event that occurs every Friday, 8am-9:00 AM,
starting June 1, 1997, ending December 31, 1997.
BEGIN:VTIMEZONE
TZID:US-Eastern
LAST-MODIFIED:19870101T000000Z
BEGIN:STANDARD
DTSTART:19971026T020000
RDATE:19971026T020000
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:19971026T020000
RDATE:19970406T020000
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
END:DAYLIGHT
END:VTIMEZONE
This is a simple example showing the current time zone rules for the
Eastern United States using a RRULE recurrence pattern. Note that
there is no effective end date to either of the Standard Time or
Daylight Time rules. This information would be valid for a recurring
event starting today and continuing indefinitely.
BEGIN:VTIMEZONE
TZID:US-Eastern
LAST-MODIFIED:19870101T000000Z
TZURL:http://zones.stds_r_us.net/tz/US-Eastern
BEGIN:STANDARD
DTSTART:19671029T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:19870405T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
END:DAYLIGHT
END:VTIMEZONE
This is an example showing a fictitious set of rules for the Eastern
United States, where the Daylight Time rule has an effective end date
(i.e., after that date, Daylight Time is no longer observed).
BEGIN:VTIMEZONE
TZID:US--Fictitious-Eastern
LAST-MODIFIED:19870101T000000Z
BEGIN:STANDARD
DTSTART:19671029T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:19870405T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4;UNTIL=19980404T070000Z
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
END:DAYLIGHT
END:VTIMEZONE
This is an example showing a fictitious set of rules for the Eastern
United States, where the first Daylight Time rule has an effective
end date. There is a second Daylight Time rule that picks up where
the other left off.
BEGIN:VTIMEZONE
TZID:US--Fictitious-Eastern
LAST-MODIFIED:19870101T000000Z
BEGIN:STANDARD
DTSTART:19671029T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
TZNAME:EST
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:19870405T020000
RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4;UNTIL=19980404T070000Z
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
END:DAYLIGHT
BEGIN:DAYLIGHT
DTSTART:19990424T020000
RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=4
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
TZNAME:EDT
END:DAYLIGHT
END:VTIMEZONE
4.6.6 Alarm Component
Component Name: VALARM
Purpose: Provide a grouping of component properties that define an
alarm.
Formal Definition: A "VALARM" calendar component is defined by the
following notation:
alarmc = "BEGIN" ":" "VALARM" CRLF
(audioprop / dispprop / emailprop / procprop)
"END" ":" "VALARM" CRLF
audioprop = 2*(
; 'action' and 'trigger' are both REQUIRED,
; but MUST NOT occur more than once
action / trigger /
; 'duration' and 'repeat' are both optional,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat /
; the following is optional,
; but MUST NOT occur more than once
attach /
; the following is optional,
; and MAY occur more than once
x-prop
)
dispprop = 3*(
; the following are all REQUIRED,
; but MUST NOT occur more than once
action / description / trigger /
; 'duration' and 'repeat' are both optional,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat /
; the following is optional,
; and MAY occur more than once
*x-prop
)
emailprop = 5*(
; the following are all REQUIRED,
; but MUST NOT occur more than once
action / description / trigger / summary
; the following is REQUIRED,
; and MAY occur more than once
attendee /
; 'duration' and 'repeat' are both optional,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat /
; the following are optional,
; and MAY occur more than once
attach / x-prop
)
procprop = 3*(
; the following are all REQUIRED,
; but MUST NOT occur more than once
action / attach / trigger /
; 'duration' and 'repeat' are both optional,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat /
; 'description' is optional,
; and MUST NOT occur more than once
description /
; the following is optional,
; and MAY occur more than once
x-prop
)
Description: A "VALARM" calendar component is a grouping of component
properties that is a reminder or alarm for an event or a to-do. For
example, it may be used to define a reminder for a pending event or
an overdue to-do.
The "VALARM" calendar component MUST include the "ACTION" and
"TRIGGER" properties. The "ACTION" property further constrains the
"VALARM" calendar component in the following ways:
When the action is "AUDIO", the alarm can also include one and only
one "ATTACH" property, which MUST point to a sound resource, which is
rendered when the alarm is triggered.
When the action is "DISPLAY", the alarm MUST also include a
"DESCRIPTION" property, which contains the text to be displayed when
the alarm is triggered.
When the action is "EMAIL", the alarm MUST include a "DESCRIPTION"
property, which contains the text to be used as the message body, a
"SUMMARY" property, which contains the text to be used as the message
subject, and one or more "ATTENDEE" properties, which contain the
email address of attendees to receive the message. It can also
include one or more "ATTACH" properties, which are intended to be
sent as message attachments. When the alarm is triggered, the email
message is sent.
When the action is "PROCEDURE", the alarm MUST include one and only
one "ATTACH" property, which MUST point to a procedure resource,
which is invoked when the alarm is triggered.
The "VALARM" calendar component MUST only appear within either a
"VEVENT" or "VTODO" calendar component. "VALARM" calendar components
cannot be nested. Multiple mutually independent "VALARM" calendar
components can be specified for a single "VEVENT" or "VTODO" calendar
component.
The "TRIGGER" property specifies when the alarm will be triggered. The "TRIGGER" property specifies a duration prior to the start of an event or a to-do. The "TRIGGER" edge may be explicitly set to be relative to the "START" or "END" of the event or to-do with the "RELATED" parameter of the "TRIGGER" property. The "TRIGGER" property value type can alternatively be set to an absolute calendar date and time of day value. In an alarm set to trigger on the "START" of an event or to-do, the "DTSTART" property MUST be present in the associated event or to-do. In an alarm in a "VEVENT" calendar component set to trigger on the "END" of the event, either the "DTEND" property MUST be present, or the "DTSTART" and "DURATION" properties MUST both be present. In an alarm in a "VTODO" calendar component set to trigger on the "END" of the to-do, either the "DUE" property MUST be present, or the "DTSTART" and "DURATION" properties MUST both be present. The alarm can be defined such that it triggers repeatedly. A definition of an alarm with a repeating trigger MUST include both the "DURATION" and "REPEAT" properties. The "DURATION" property specifies the delay period, after which the alarm will repeat. The "REPEAT" property specifies the number of additional repetitions that the alarm will triggered. This repitition count is in addition to the initial triggering of the alarm. Both of these properties MUST be present in order to specify a repeating alarm. If one of these two properties is absent, then the alarm will not repeat beyond the initial trigger. The "ACTION" property is used within the "VALARM" calendar component to specify the type of action invoked when the alarm is triggered. The "VALARM" properties provide enough information for a specific action to be invoked. It is typically the responsibility of a "Calendar User Agent" (CUA) to deliver the alarm in the specified fashion. An "ACTION" property value of AUDIO specifies an alarm that causes a sound to be played to alert the user; DISPLAY specifies an alarm that causes a text message to be displayed to the user; EMAIL specifies an alarm that causes an electronic email message to be delivered to one or more email addresses; and PROCEDURE specifies an alarm that causes a procedure to be executed. The "ACTION" property MUST specify one and only one of these values. In an AUDIO alarm, if the optional "ATTACH" property is included, it MUST specify an audio sound resource. The intention is that the sound will be played as the alarm effect. If an "ATTACH" property is specified that does not refer to a sound resource, or if the specified sound resource cannot be rendered (because its format is unsupported, or because it cannot be retrieved), then the CUA or other entity responsible for playing the sound may choose a fallback
action, such as playing a built-in default sound, or playing no sound
at all.
In a DISPLAY alarm, the intended alarm effect is for the text value
of the "DESCRIPTION" property to be displayed to the user.
In an EMAIL alarm, the intended alarm effect is for an email message
to be composed and delivered to all the addresses specified by the
"ATTENDEE" properties in the "VALARM" calendar component. The
"DESCRIPTION" property of the "VALARM" calendar component MUST be
used as the body text of the message, and the "SUMMARY" property MUST
be used as the subject text. Any "ATTACH" properties in the "VALARM"
calendar component SHOULD be sent as attachments to the message.
In a PROCEDURE alarm, the "ATTACH" property in the "VALARM" calendar
component MUST specify a procedure or program that is intended to be
invoked as the alarm effect. If the procedure or program is in a
format that cannot be rendered, then no procedure alarm will be
invoked. If the "DESCRIPTION" property is present, its value
specifies the argument string to be passed to the procedure or
program. "Calendar User Agents" that receive an iCalendar object with
this category of alarm, can disable or allow the "Calendar User" to
disable, or otherwise ignore this type of alarm. While a very useful
alarm capability, the PROCEDURE type of alarm SHOULD be treated by
the "Calendar User Agent" as a potential security risk.
Example: The following example is for a "VALARM" calendar component
that specifies an audio alarm that will sound at a precise time and
repeat 4 more times at 15 minute intervals:
BEGIN:VALARM
TRIGGER;VALUE=DATE-TIME:19970317T133000Z
REPEAT:4
DURATION:PT15M
ACTION:AUDIO
ATTACH;FMTTYPE=audio/basic:ftp://host.com/pub/sounds/bell-01.aud
END:VALARM
The following example is for a "VALARM" calendar component that
specifies a display alarm that will trigger 30 minutes before the
scheduled start of the event or the due date/time of the to-do it is
associated with and will repeat 2 more times at 15 minute intervals:
BEGIN:VALARM
TRIGGER:-PT30M
REPEAT:2
DURATION:PT15M
ACTION:DISPLAY
DESCRIPTION:Breakfast meeting with executive\n
team at 8:30 AM EST.
END:VALARM
The following example is for a "VALARM" calendar component that
specifies an email alarm that will trigger 2 days before the
scheduled due date/time of a to-do it is associated with. It does not
repeat. The email has a subject, body and attachment link.
BEGIN:VALARM
TRIGGER:-P2D
ACTION:EMAIL
ATTENDEE:MAILTO:john_doe@host.com
SUMMARY:*** REMINDER: SEND AGENDA FOR WEEKLY STAFF MEETING ***
DESCRIPTION:A draft agenda needs to be sent out to the attendees
to the weekly managers meeting (MGR-LIST). Attached is a
pointer the document template for the agenda file.
ATTACH;FMTTYPE=application/binary:http://host.com/templates/agen
da.doc
END:VALARM
The following example is for a "VALARM" calendar component that
specifies a procedural alarm that will trigger at a precise date/time
and will repeat 23 more times at one hour intervals. The alarm will
invoke a procedure file.
BEGIN:VALARM
TRIGGER;VALUE=DATE-TIME:19980101T050000Z
REPEAT:23
DURATION:PT1H
ACTION:PROCEDURE
ATTACH;FMTTYPE=application/binary:ftp://host.com/novo-
procs/felizano.exe
END:VALARM
(page 73 continued on part 3)
