httpequivXUACompatible

httpequivXUACompatible is a term used to refer to the HTML http-equiv directive X-UA-Compatible, a mechanism that was used to influence how Internet Explorer renders a document. The directive can be supplied in two ways: as a meta tag in the HTML head or as an HTTP header sent by the server.

The most common HTML form is a meta tag such as <meta http-equiv="X-UA-Compatible" content="IE=edge">, which instructs IE to use the highest available standards mode. Other values include IE=9 or IE=EmulateIE8, which request specific compatibility modes. When X-UA-Compatible is provided as an HTTP header, the corresponding response header X-UA-Compatible: IE=edge achieves the same effect, and the HTTP header takes precedence over a meta tag if both are present.

In HTML, the meta tag should appear inside the head element. It is typically placed as the first meta tag in head, after the charset declaration if present, to ensure reliable interpretation by older browsers.

Support and relevance: X-UA-Compatible is a non-standard directive that originated to address rendering differences in older Internet Explorer versions. It is largely ignored by modern browsers, and its practical use has diminished with the phasing out of IE and the rise of Edge. Nevertheless, some legacy sites and certain enterprise applications continue to rely on it to force specific rendering modes for compatibility reasons.

See also: Quirks mode, Standards mode, Doctype, Compatibility view.