[1] RFC 6993 - Instant Messaging and Presence Purpose for the Call-Info Header Field in the Session Initiation Protocol (SIP) ( (2013-07-31 00:03:05 +09:00 版)) <http://tools.ietf.org/html/rfc6993>

[2] Fix: parsing image purpose (closes #513, #511) (mounirlamouri著, 2016-11-03 12:19:45 +09:00) <https://github.com/w3c/manifest/commit/9cdfcfa0f901413d201f491de8e2259de37c78dc>

[3] When purpose is invalid, return set with "any" instead of undefined (… (mounirlamouri著, 2016-11-03 13:33:31 +09:00) <https://github.com/w3c/manifest/commit/9f2f69484062e483a08817db497c53d6260164c4>