Calendar:Recurrence and Exceptions

Recurring and repeating items need to allow the user to modify properties of specific occurrences, but still allow the rest to be tied in to the main parent item. For example, a weekly meeting could have its location or time changed for one week, but modifying the attendees should change all occurrences.

How does one express this relationship with ics?

RECURRENCE-ID as a DATE-TIME is used to refer to an explicit occurrence. It is used as the effective DTSTART of the occurrence.

DTSTART and UID should be the same across all occurrences of an item.

Some platforms, notably Outlook and Lotus Notes do strange things with this, including setting DTSTART and RECURRENCE-ID to be the same. The UID still refers to the parent, however, so we should rely on UID, and should just ignore DTSTART for occurrences.

What do we do currently?

Current calendar code supports recurring/repeating events, as well as exceptions. However, only the base event is parsed. There is no support for occurrences-with-changes.

Do caldav servers/ics clients support the full RECURRENCE-ID/DTSTART/UID mechanism?

Need some ICS to test this, and see what they round trip as.