[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
[RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)",
RFC 5545, DOI 10.17487/RFC5545, September 2009,
[RFC5546] Daboo, C., Ed., "iCalendar Transport-Independent
Interoperability Protocol (iTIP)", RFC 5546,
DOI 10.17487/RFC5546, December 2009,
[W3C.REC-css3-color-20110607]
Celik, T., Lilley, C., and D. Baron, "CSS Color Module
Level 3", World Wide Web Consortium Recommendation
REC-css3-color-20110607, June 2011,