I have an application that produces an iCalendar feed (RFC 5545). The calendar feed works on Google Calendar and on Android but I have been getting reports that it isn't working on OS X Calendar (aka iCal). The calendar feed currently uses the RDATE element extensively and validates.
Does iCal support the RDATE element?
UPDATE
I have managed to get recurrence working on Apple devices by using RRULE with EXDATEs. The problem is this does not work properly on Android devices. (Argghhh!)
Best Answer
I have not run exhaustive tests but empirically I have concluded that Apple products do not implement the RDATE recurrence rule.
Apple products do appear to implement the RRULE but only a limited subset of this. The extent to which the RRULE is supported might be deduced from the options available for setting recurring events in Apple apps. It should be possible to support simple patterns (every day, every week, every 2 weeks, every month, every year) but probably not more complex patterns using BYMONTHDAY, BYYEARDAY, BYWEEKNO, BYMONTH, BYSETPOS.
I've noticed that Google Calendar might display a full recurrence set whereas an Apple device that is synced from that calendar will only show the first event.
I would welcome a more authoritative answer.