HTTP とか SIP とかだと、複数頭領域を読点区切りで単一頭領域にまとめることが
出来ます。

まとめられる頭領域:

-[[Accept:領域]] ([[HTTP/1.1]])
-[[Accept-Charset:領域]] ([[HTTP/1.1]])
-[[Accept-Encoding:領域]] ([[HTTP/1.1]])
-[[Accept-Language:領域]] ([[HTTP/1.1]])
-[[Accept-Ranges:領域]] ([[HTTP/1.1]])
-[[Allow:領域]] ([[HTTP]], [[SIP]])
-[[Cache-Control:領域]] ([[HTTP/1.1]])
-[[Connection:領域]] ([[HTTP/1.1]])
-[[Contact:領域]] (m:) ([[SIP]])
-[[Content-Encoding:領域]] (e:) ([[HTTP/1.1]], [[SIP]])
-[[Content-Language:領域]] ([[HTTP/1.1]])
-[[Expect:領域]] ([[HTTP/1.1]])
-[[If-Match:領域]] ([[HTTP/1.1]])
-[[If-None-Match:領域]] ([[HTTP/1.1]])
-[[Keep-Alive:領域]] ([[HTTP/1.1]] [[RFC2068]])
-[[Link:領域]] ([[HTTP/1.1]] [[RFC2068]])
-[[Public:領域]] ([[HTTP/1.1]] [[RFC2068]])
-[[Pragma:領域]] ([[HTTP]])
-[[Proxy-Authenticate:領域]] ([[HTTP/1.1]])
-[[Record-Route:領域]] ([[SIP]])
-[[Require:領域]] ([[SIP]])
-[[Route:領域]] ([[SIP]])
-[[TE:領域]] ([[HTTP/1.1]])
-[[Trailer:領域]] ([[HTTP/1.1]])
-[[Transfer-Encoding:領域]] ([[HTTP/1.1]])
-[[Unsupported:領域]] ([[SIP]])
-[[Upgrade:領域]] ([[HTTP/1.1]])
-[[URI:領域]] ([[HTTP/1.1]] [[RFC2068]])
-[[Vary:領域]] ([[HTTP/1.1]])
-[[Via:領域]] (v:) ([[HTTP/1.1]], [[SIP]])
-[[Warning:領域]] ([[HTTP/1.1]], [[SIP]])
-[[WWW-Authenticate:領域]] ([[HTTP]])



*RFC 2616 HTTP/1.1 4.2 から抜粋

   Multiple message-header fields with the same field-name MAY be
   present in a message if and only if the entire field-value for that
   header field is defined as a comma-separated list [i.e., #(values)].
   It MUST be possible to combine the multiple header fields into one
   "field-name: field-value" pair, without changing the semantics of the
   message, by appending each subsequent field-value to the first, each
   separated by a comma. The order in which header fields with the same
   field-name are received is therefore significant to the
   interpretation of the combined field value, and thus a proxy MUST NOT
   change the order of these field values when a message is forwarded.

*See also
-[[メッセージの頭]]
--[[RFC822と仲間達の頭領域名]]
-[[HTTP]]

*License

See [[RFCのライセンス]]