[1] RFC 7809 - Calendaring Extensions to WebDAV (CalDAV): Time Zones by Reference (2016-04-02 09:16:11 +09:00 版) https://tools.ietf.org/html/rfc7809

[2] RFC 5545 - Internet Calendaring and Scheduling Core Object Specification (iCalendar) ( (2016-06-19 16:13:42 +09:00)) https://tools.ietf.org/html/rfc5545#section-3.6.5

[3] RFC 4791 - Calendaring Extensions to WebDAV (CalDAV) (2017-09-24 16:22:36 +09:00) https://tools.ietf.org/html/rfc4791#section-4.1