[1] RFC 5546 - iCalendar Transport-Independent Interoperability Protocol (iTIP) ( (5/8/2011, 6:25:12 AM 版)) <http://tools.ietf.org/html/rfc5546>
[2] RFC 5546 - iCalendar Transport-Independent Interoperability Protocol (iTIP) (4/19/2015, 7:20:38 AM 版) <https://tools.ietf.org/html/rfc5546>
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