This property specifies when an alarm will trigger.
The default value type is DURATION. The value type can be set to a DATE-TIME value type, in which case the value MUST specify a UTC-formatted DATE-TIME value. Property Parameters: IANA, non-standard, value data type, time zone identifier, or trigger relationship property parameters can be specified on this property. The trigger relationship property parameter MUST only be specified when the value type is "DURATION".
This property MUST be specified in the "VALARM" calendar component.
This property defines when an alarm will trigger. The default value type is DURATION, specifying a relative time for the trigger of the alarm. The default duration is relative to the start of an event or to-do with which the alarm is associated. The duration can be explicitly set to trigger from either the end or the start of the associated event or to-do with the "RELATED" parameter. A value of START will set the alarm to trigger off the start of the associated event or to-do. A value of END will set the alarm to trigger off the end of the associated event or to-do.
Either a positive or negative duration may be specified for the "TRIGGER" property. An alarm with a positive duration is triggered after the associated start or end of the event or to-do. An alarm with a negative duration is triggered before the associated start or end of the event or to-do.
The "RELATED" property parameter is not valid if the value type of the property is set to DATE-TIME (i.e., for an absolute date and time alarm trigger). If a value type of DATE-TIME is specified, then the property value MUST be specified in the UTC time format. If an absolute trigger is specified on an alarm for a recurring event or to-do, then the alarm will only trigger for the specified absolute DATE-TIME, along with any specified repeating instances.
If the trigger is set relative to START, then the "DTSTART" property MUST be present in the associated "VEVENT" or "VTODO" calendar component. If an alarm is specified for an event with the trigger set relative to the END, then the "DTEND" property or the "DTSTART" and "DURATION " properties MUST be present in the associated "VEVENT" calendar component. If the alarm is specified for a to-do with a trigger set relative to the END, then either the "DUE" property or the "DTSTART" and "DURATION " properties MUST be present in the associated "VTODO" calendar component.
Alarms specified in an event or to-do that is defined in terms of a DATE value type will be triggered relative to 00:00:00 of the user's configured time zone on the specified date, or relative to 00:00:00 UTC on the specified date if no configured time zone can be found for the user. For example, if "DTSTART" is a DATE value set to 19980205 then the duration trigger will be relative to 19980205T000000 America/New_York for a user configured with the America/New_York time zone.
This property is defined by the following notation:
trigger = "TRIGGER" (trigrel / trigabs) CRLF
trigrel = *( ; ; The following are OPTIONAL, ; but MUST NOT occur more than once. ; (";" "VALUE" "=" "DURATION") / (";" trigrelparam) / ; ; The following is OPTIONAL, ; and MAY occur more than once. ; (";" other-param) ; ) ":" dur-value
trigabs = *( ; ; The following is REQUIRED, ; but MUST NOT occur more than once. ; (";" "VALUE" "=" "DATE-TIME") / ; ; The following is OPTIONAL, ; and MAY occur more than once. ; (";" other-param) ; ) ":" date-time
A trigger set 15 minutes prior to the start of the event or to-do.
A trigger set five minutes after the end of an event or the due date of a to-do.
A trigger set to an absolute DATE-TIME.
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