* 仕様書

[REFS[
- [4] 
[CITE@en[[[RFC 3458]] - Message Context for Internet Mail]], [TIME[2021-04-11T11:20:22.000Z]], [TIME[2021-04-23T12:08:42.681Z]] <https://tools.ietf.org/html/rfc3458>
]REFS]

* BNF

;; draft-ietf-vpim-hint-07 をもとに作成。

[PRE[
 Message-Context = "Message-Context:" message-context-class
 message-context-class = ( "voice-message" 
                         / "fax-message" 
                         / "pager-message" 
                         / "multimedia-message" 
                         / "text-message" 
                         / "none" 
                         / extension-type ) 
 extension-type = token  ; Defined and registered type 
                / vnd.token ; Experimental, private use 
 token = mime-token	;; not starting with the characters "vnd."> 
 vnd.token = "vnd." token	;; Vendor-specific, private token
]PRE]

;; vnd. は無登録の仕様 token らしい。いいのか? そして x- は無しかい。

* 歴史

- <urn:ietf:id:draft-ietf-vpim-hint-07>
- [1] [CODE[Message-Context:]] は [[RFC3458]] になりました。
- [2] [[[IANAREG]]] ''Context labels for Internet Messages'' <http://www.iana.org/assignments/message-header-types>

[3]
[[RFC 3938]] [CITE[Video-Message Message-Context]]:
RFC 3458 から [CODE(822)[video-message]] が独立しました。

[5] [CITE@en[rfc3938]], [TIME[2021-06-22T04:07:47.000Z]] <https://datatracker.ietf.org/doc/html/rfc3938>