Extensible Markup Language (XML) -- A markup language similar to HTML, but allowing the definition of additional elements within a document. Markup languages specify what document elements are rather than how to handle them. Hypertext Markup Language (HTML) -- the description language used for web pages -- is the most widely used. HTML however, is restricted to predefined language elements.

XML is similar to HTML but allows additional language elements to be defined in documents. Handling of new elements is, of course, constrained to the handling that can be specified using built in language capabilities. XML is being hyped as a simplified, web oriented, version of the Standardized General Markup Language (SGML). It appears to be a subset of SGML.

The primary utility of XML is predicated to be for applications like search engines and for industry specific applications where increased knowledge of document content and better identification of elements may be useful. Thus, for example one could presumably define a <SKU> (Stock keeping Unit) element, define its handling, then use it in a document where it can be differentiated from other Bold or Header or paragraph break marked items. Other than that, I have found no explanation of why anyone should care about XML or use it in preference to HTML.

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