Within certain document media types, the base URL of the document can be embedded within the content itself such that it can be readily obtained by a parser. This can be useful for descriptive documents, such as tables of content, which may be transmitted to others through protocols other than their usual retrieval context (e.g., E-Mail or USENET news).

   It is beyond the scope of this document to specify how, for each
   media type, the base URL can be embedded.  It is assumed that user
   agents manipulating such media types will be able to obtain the
   appropriate syntax from that media type's specification.  An example
   of how the base URL can be embedded in the Hypertext Markup Language
   (HTML) [3] is provided in an Appendix (Section 10).

Messages are considered to be composite documents. The base URL of a message can be specified within the message headers (or equivalent tagged metainformation) of the message. For protocols that make use of message headers like those described in RFC 822 [5], we recommend that the format of this header be:

メッセージは合成文書と考えられます。メッセージの基底 URL をメッセージの頭 (あるいは同様の札つきメタ情報) の中に指定出来ます。 RFC 822 で説明されているようなメッセージ頭を使うプロトコルでは、 この頭の形式をこんな風にするのを推奨します。

      base-header  = "Base" ":" "<URL:" absoluteURL ">"

where "Base" is case-insensitive and any whitespace (including that used for line folding) inside the angle brackets is ignored. For example, the header field

ここで、 "Base" は大文字・小文字を区別せず、角括弧中の空白間隔 (行折畳みに使われるものを含む) は全て無視されます。例えば、頭欄

      Base: <URL:http://www.ics.uci.edu/Test/a/b/c>

would indicate that the base URL for that message is the string "http://www.ics.uci.edu/Test/a/b/c". The base URL for a message serves as both the base for any relative URLs within the message headers and the default base URL for documents enclosed within the message, as described in the next section.

はメッセージの基底 URL が "" であることを示します。メッセージの基底 URI はメッセージ頭中の相対 URL の基底とメッセージに囲まれている文書の 既定の基底 URI の両方になります。詳しくは次の節で説明します。

Protocols which do not use the RFC 822 message header syntax, but which do allow some form of tagged metainformation to be included within messages, may define their own syntax for defining the base URL as part of a message.

RFC 822 メッセージ頭構文を使わないが何らかの形の札付けしたメタ情報をメッセージ中に含めることが出来るプロトコルでは、基底 URI をメッセージの一部として定義するそれぞれの構文を定義しても構いません。

A "Content-Base:" or a "Content-Location:" header in the response.

For backwards compatibility with older HTTP implementations we will also look for the "Base:" header.