Extensible Markup Language (XML), like HTML, allows you to apply markup, in the form of tags, to a document. However, unlike HTML, XML is designed to be used as a generalized markup language. In other words, markup applied to an XML document can be used to convey not only display and formatting information as with HTML, but semantic and organizational structure for the document. This flexibility makes XML extremely powerful, and the possible range of applications is impressive.
For more information on Microsoft's work with XML, refer to the XML SDK, available on MSDN Online at http://msdn.microsoft.com/xml/. For more detailed information about XML and related standards, see the World Wide Web Consortium at http://www.w3.org.