Common validation for all iTIP methods.
Component/Property Presence
------------------- ----------------------------------------------
VTIMEZONE 0+ MUST be present if any date/time refers
to timezone
DAYLIGHT 0+ MUST be one or more of either STANDARD or
DAYLIGHT
COMMENT 0 or 1
DTSTART 1 MUST be local time format
RDATE 0+ if present RRULE MUST NOT be present
RRULE 0+ if present RDATE MUST NOT be present
TZNAME 0 or 1
TZOFFSET 1
TZOFFSETFROM 1
TZOFFSETTO 1
X-PROPERTY 0+
LAST-MODIFIED 0 or 1
STANDARD 0+ MUST be one or more of either STANDARD or
DAYLIGHT
COMMENT 0 or 1
DTSTART 1 MUST be local time format
RDATE 0+ if present RRULE MUST NOT be present
RRULE 0+ if present RDATE MUST NOT be present
TZNAME 0 or 1
TZOFFSETFROM 1
TZOFFSETTO 1
X-PROPERTY 0+
TZID 1
TZURL 0 or 1
X-PROPERTY 0+