mhical rejects things like -1SU (last Sunday in the month), despite its presence (at a cursory glance) in the ical standard:
sbr/datetime.c:295: if (*cp == '+') { ++cp; } /* +n specific day; don't support '-' */ else if (*cp == '-') { goto fail; } .. so RRULEs like "FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU," fail. Is this just a "not yet implemented", so possibly worth my trying to add? Conrad