A programming language/specification developed by the W3C. XML is a pared-down version of SGML, designed especially for Web documents. It enables Web authors and Web developers to create their own customized tags to provide functionality not available with HTML. For example, XML supports links that point to multiple documents (as opposed to HTML links, which can reference just one destination each).
XML provides a powerful set of tools for developing a new generation of Web applications, including tools like database exchange, distribution of processing to clients, multiple views of data, intelligent agents, management of document collections, and so on. Whether XML eventually supplants HTML as the standard Web formatting specification depends a lot on whether it is supported by future Web browsers.
Also, XML is a lot more abstract and complex than HTML, and unlike HTML, it isn't immediately gratifying in terms of creating Web pages. So now there is XHTML, a bridge between HTML and XML that is useful and will help Web builders conquer any fears of XML. VoiceXML is an extension that defines how voice-interaction systems (such as voice recognition) interact with the Internet. For example, VoiceXML makes it possible for users to interact with Web servers simply by talking on the phone (see: voice portal).