RFC 5545 3.8.5 Recurrence Component Properties lists
RRULE 3.8.5.3 (added to PIM earlier)
EXDATE 3.8.5.1 (added to PIM via-545 )
RDATE 3.8.5.2 (not in current request lists, and more complex - DateTime, set to Date or Period) - seems to have a TypeType for DATE-TIME, DATE, PERIOD, other-param
The form of RDATE and EXDATE are similar, and based on DateTime