The META element can be used within the HEAD element to embed document metainformation not defined by other HTML elements. Such information can be extracted by servers/clients for use in identifying, indexing, and cataloging specialized document metainformation.
Although it is generally preferable to use named elements which have well-defined semantics for each type of metainformation (e.g. TITLE), this element is provided for situations where strict SGML parsing is necessary and the local DTD is not extensible.
In addition, HTTP servers can read the content of the document HEAD to generate response headers corresponding to any elements defining a value for the attribute HTTP-EQUIV. This provides document authors a mechanism (not necessarily the preferred one) for identifying information which should be included in the response headers for an HTTP request.
The attributes of the META element are:
If the document contains:
<expires http-equiv="Expires">Tue, 04 Dec 1993 21:29:02 GMT</expires> <meta http-equiv="Keywords" content="Fred, Barney, Wilma"> <meta http-equiv="Reply-to" content="firstname.lastname@example.org (Roy Fielding)">The server may include the headers:
Expires: Tue, 04 Dec 1993 21:29:02 GMT Keywords: Fred, Barney, Wilma Reply-to: email@example.com (Roy Fielding)as part of the HTTP response to a GET or HEAD request for that document.
When the HTTP-EQUIV attribute is not present, the server should not generate an HTTP response header for this metainformation; e.g.,
<meta name="IndexType" content="Service">would not generate an HTTP response header but would still allow clients or other tools to make use of that metainformation.
One example of an inappropriate usage for the META element is to use it to define information that should be associated with an already existing HTML element, e.g.
<meta name="Title" content="The Etymology of Dunsel">
A second example of inappropriate usage is to name an HTTP-EQUIV equal to a response header that should normally only be generated by the HTTP server. Example names that are inappropriate include "Server", "Date", and "Last-modified" -- the exact list of inappropriate names is dependent on the particular server implementation. It is recommended that servers ignore any META elements which specify http-equivalents which are equal (case-insensitively) to their own reserved response headers.From: "Roy T. Fielding" <fielding@simplon.ICS.UCI.EDU>