Component/Property Presence
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METHOD 1 MUST be "REPLY"
VTODO 1+ All component MUST have the same UID
ATTENDEE 1+
DTSTAMP 1
ORGANIZER 1
UID 1 MUST must be the address of the replying
attendee
REQUEST-STATUS 0+
ATTACH 0+
CATEGORIES 0 or 1 This property may contain a list of values
CLASS 0 or 1
COMMENT 0 or 1
CONTACT 0+
CREATED 0 or 1
DESCRIPTION 0 or 1
DTSTART 0 or 1
DUE 0 or 1 If present DURATION MUST NOT be present
DURATION 0 or 1 If present DUE MUST NOT be present
EXDATE 0+
EXRULE 0+
GEO 0 or 1
LAST-MODIFIED 0 or 1
LOCATION 0 or 1
PERCENT-COMPLETE 0 or 1
PRIORITY 0 or 1
RDATE 0+
RELATED-TO 0+
RESOURCES 0 or 1 This property may contain a list of values
RRULE 0+
RECURRENCE-ID 0 or 1 MUST only if referring to an instance of a
Recurring calendar component. Otherwise it
MUST NOT be present
SEQUENCE 0 or 1 MUST be the sequence number of
the original REQUEST if greater than 0.
MAY be present if 0.
STATUS 0 or 1
SUMMARY 0 or 1 Can be null
URL 0 or 1
X-PROPERTY 0+
VTIMEZONE 0 or 1 MUST be present if any date/time refers to
a timezone
X-COMPONENT 0+
VALARM 0
VEVENT 0
VFREEBUSY 0