Standard Format for Representing Time Recurrence/Schedules?

Question

I'm aware of iCal's RECUR value but I'm not sure how flexible it is. Are there any other formats that can represent arbitrarily complex recurrence schedules? I'd like to use a standard because the component I'm writing is meant to interface with other applications I've written and ideally third party applications.

Something like:

start: date/time/time zone
repeat: every 2nd Monday, 3rd Tuesday, and all weekends
except: specific date
end: date/time/time zone
start again: ... etc

or

repeat: 1pm-2pm, 4pm-5pm every MWF
end: date/time/time zone