[1] RFC 5546 - iCalendar Transport-Independent Interoperability Protocol (iTIP) ( (2011-05-08 15:25:12 +09:00 版)) <http://tools.ietf.org/html/rfc5546>

[2] RFC 5546 - iCalendar Transport-Independent Interoperability Protocol (iTIP) (2015-04-19 16:20:38 +09:00 版) <https://tools.ietf.org/html/rfc5546>