4.2. Part 2. Specific Implementation Information

This table contains elements for specific rules from RFC 2445. For each one, please indicate whether the implementation does (Yes) or does not (No) conform to the stated rule. If you have comments, issues or questions about this rule please enter in the Comment line under the rule.

RFC 2445 — iCalendar elements
4.3.10.a Recurrence Rule ○ Yes ○ No ○ Other	`MUST`	Individual rule parts `MUST` only be specified once.
4.3.10.b Recurrence Rule ○ Yes ○ No ○ Other	`MUST`	The `FREQ` rule part identifies the type of recurrence rule. This rule part `MUST` be specified in the recurrence rule.
4.3.10.c Recurrence Rule ○ Yes ○ No ○ Other	`MUST`	If `UNTIL` is specified as a date-time value, then it `MUST` be specified in a UTC time format.
4.3.10.d Recurrence Rule ○ Yes ○ No ○ Other	`MUST`	`BYSETPOS` `MUST` only be used in conjunction with another `BYxxx` rule part.
4.6.1.a Event Component ○ Yes ○ No ○ Other	`MUST NOT`	The following are optional but `MUST NOT` occur more than once: class / created / description / dtstart / geo / last-mod / location / organizer / priority / dstamp / seq / status / summary / transp / uid / url / recurid.
4.6.1.b Event Component ○ Yes ○ No ○ Other	`MAY`	The following are optional and `MAY` occur more than once: attach / attendee / categories / comment / contact / exdate / exrule / rstatus / related / resources / rdate / rrule / x-pro.
4.6.2.a To-do Component ○ Yes ○ No ○ Other	`MUST NOT`	The following are optional, but `MUST NOT` occur more than once: class / completed / created / description / dstamp / dtstart / geo / last-mod / location / organizer / percent / priority / recurid / seq / status / summary / uid / ur.
4.6.2.b To-do Component ○ Yes ○ No ○ Other	`MAY`	The following are optional, and `MAY` occur more than once: attach / attendee / categories / comment / contact / exdate / exrule / rstatus / related / resources / rdate / rrule / x-pro.
4.6.3.a Journal Component ○ Yes ○ No ○ Other	`MUST NOT`	The following are optional, but `MUST NOT` occur more than once: class / created / description / dtstart / dstamp / last-mod / organizer / recurid / seq / status / summary / uid / url.
4.6.3.b Journal Component ○ Yes ○ No ○ Other	`MAY`	The following are optional, and `MAY` occur more than once: attach / attendee / categories / comment / contact / exdate / exrule / related / rdate / rrule / rstatus / x-pro.
4.6.4.a Free/Busy Component ○ Yes ○ No ○ Other	`MUST NOT`	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.
4.6.5.a Time Zone Component ○ Yes ○ No ○ Other	`MUST`	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.
4.6.5.b Time Zone Component ○ Yes ○ No ○ Other	`MAY`	A ‘VTIMEZONE’ calendar component `MAY` be present if the iCalendar object does not contain an `RRULE` that generates dates on both sides of a time zone shift.
4.6.5.c Time Zone Component ○ Yes ○ No ○ Other	`MUST`	If an `RRULE` that generates dates on both sides of a time zone shift is present, there `MUST` be valid time zone information for all recurrence instances.
4.6.6.a Alarm Component ○ Yes ○ No ○ Other	`MUST NOT`	‘DURATION’ and ‘REPEAT’ are both optional, and `MUST NOT` occur more than once each, but if one occurs, so `MUST` the other.
4.6.6.b Alarm Component ○ Yes ○ No ○ Other	`MUST`	A definition of an alarm with a repeating trigger `MUST` include both the ‘DURATION’ and ‘REPEAT’ properties.
4.6.6.c Alarm Component ○ Yes ○ No ○ Other	`MUST`	Both ‘DURATION’ and ‘REPEAT’ 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.
4.8.4.4.a Recurrence ID ○ Yes ○ No ○ Other	`MUST`	If the value of the ‘DTSTART’ property is a ‘DATE’ type value, then the value `MUST` be the calendar date for the recurrence instance.
4.8.4.4.b Recurrence ID ○ Yes ○ No ○ Other	`MUST NOT`	The following are optional, but `MUST NOT` occur more than once: “VALUE” “=” (“DATE-TIME” / “DATE”), tzidparam, rangeparam.
4.8.4.4.c Recurrence ID ○ Yes ○ No ○ Other	`MAY`	The following are optional, and `MAY` occur more than once: xparam.
4.8.5.1.a Exception Date/Times ○ Yes ○ No ○ Other	`MUST`	The “EXDATE” property can be used to exclude the value specified in “DTSTART”. However, in such cases the original “DTSTART” date `MUST` still be maintained by the calendaring and scheduling system because the original “DTSTART” value has inherent usage dependencies by other properties such as the “RECURRENCE-ID”.
4.8.5.1.b Exception Date/Times ○ Yes ○ No ○ Other	`MUST NOT`	The following are optional, but `MUST NOT` occur more than once: “VALUE” “=” (“DATE-TIME” / “DATE”), tzidparam.
4.8.5.1.c Exception Date/Times ○ Yes ○ No ○ Other	`MAY`	The following is optional, and `MAY` occur more than once: xparam.
4.8.5.3.a Recurrence Date/Times ○ Yes ○ No ○ Other	`MUST NOT`	The following are optional, but `MUST NOT` occur more than once: “VALUE” “=” (“DATE-TIME” / “DATE” / “PERIOD”), tzidparam.
4.8.5.3.b Recurrence Date/Times ○ Yes ○ No ○ Other	`MAY`	The following is optional, and `MAY` occur more than once: xparam.
4.8.5.4.a Recurrence Rule ○ Yes ○ No ○ Other	`MUST`	Any duration associated with the iCalendar object applies to all members of the generated recurrence set. Any modified duration for specific recurrences `MUST` be explicitly specified using the “RDATE” property.
4.8.7.4.a Sequence Number ○ Yes ○ No ○ Other	`MUST`	When the “Organizer” makes changes to one of the following properties, the sequence number `MUST` be incremented: “DTSTART”, “DTEND”, “DUE”, “RDATE”, “RRULE”, “EXDATE”, “EXRULE”, “STATUS”.
RFC 2446 — iTIP elements
3.2.4.a `VEVENT CANCEL` ○ Yes ○ No ○ Other	`MUST`	To cancel the complete range of a recurring event, the “UID” property value for the event `MUST` be specified and a “RECURRENCE-ID” `MUST NOT` be specified in the “CANCEL” method.
3.2.4.b `VEVENT CANCEL` ○ Yes ○ No ○ Other	`MUST`	In order to cancel an individual instance of the event, the “RECURRENCE-ID” property value for the event `MUST` be specified in the “CANCEL” method.
3.2.4.c `VEVENT CANCEL` ○ Yes ○ No ○ Other	`MUST`	Cancelling multiple `VEVENT` instances `MUST` be done with either “RECURRENCE-ID” and “RANGE” `OR` multiple “RECURRENCE-ID” values.
3.4.5.a `VTODO CANCEL` ○ Yes ○ No ○ Other	`MUST`	To cancel the complete range of a recurring “VTODO” calendar component, the “UID” property value for the “VTODO” calendar component `MUST` be specified and a “RECURRENCE-ID” `MUST NOT` be specified in the “CANCEL” method.
3.4.5.b `VTODO CANCEL` ○ Yes ○ No ○ Other	`MUST`	In order to cancel an individual instance of a recurring “VTODO” calendar component, the “RECURRENCE-ID” property value for the “VTODO” calendar component `MUST` be specified in the “CANCEL” method.
3.4.6.a `VTODO REFRESH` ○ Yes ○ No ○ Other	`MUST`	A refresh of a recurrence instance of a “VTODO” calendar component may be requested by specifying the “RECURRENCE-ID” property corresponding to the associated “VTODO” calendar component. The “Organizer” responds with the latest description and rendition of the “VTODO” calendar component. In most cases this will be a `REQUEST` unless the “VTODO” has been cancelled, in which case the `ORGANIZER` must send a “CANCEL”. This method is intended to facilitate machine processing of requests for updates to a “VTODO” calendar component.
3.5.3.a `VJOURNAL CANCEL` ○ Yes ○ No ○ Other	`MUST`	To cancel the complete range of a recurring journal entry, the “UID” property value for the journal entry `MUST` be specified and a “RECURRENCE-ID” property `MUST NOT` be specified in the “CANCEL” method.
3.5.3.b `VJOURNAL CANCEL` ○ Yes ○ No ○ Other	`MUST`	In order to cancel an individual instance of the journal entry, the “RECURRENCE-ID” property value for the journal entry `MUST` be specified in the “CANCEL” method.