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Monday, April 6, 2009

<meta http-equiv

Maps the tags and their respective names to an HTTP response header for processing. The syntax is....


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META tags with an HTTP-EQUIV attribute are equivalent to HTTP headers. Typically, they control the action of browsers, and may be used to refine the information provided by the actual headers. Tags using this form should have an equivalent effect when specified as an HTTP header, and in some servers may be translated to actual HTTP headers automatically or by a pre-processing tool.

Note: While HTTP-EQUIV META tag appears to work properly with Netscape Navigator, other browsers may ignore them, and they are ignored by Web proxies, which are becoming more widespread. Use of the equivalent HTTP header, as supported by e.g. Apache server, is more reliable and is recommended wherever possible.

HTTP headers are defined in RFC1945 (HTTP/1.0) and RFC2068 (HTTP/1.1). Note that RFC2068 states that multiple headers with the same name may be present only if the values may be concatenated.

HTTP headers may be generated by CGI scripts, and in Apache and CERN httpd by using a side file containing metadata. Other servers may have other mechanisms to generate headers. Note that certain server-generated headers may not be overridden (such as Date), and that others are only meaningful with a non-200 status code. Using an HTTP header is preferable to using META tags, since the header will be understood by cache agents and proxies in addition to browsers, and metadata (such as PICS data) may be associated with image files, sound files, etc.

However, new HTTP headers should not be created without checking for conflict with existing ones since it is possible to interfere with server and proxy operation.


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