XML

XML, the eXtensible Markup Language, is a standard of the World Wide Web Consortium (W3C). XML documents use elements (tags) known from other markup languages like HTML. Using XSL transformations XML files can be transformed into other formats like XHTML or PDF. Many common used languages are based on XML: XHTML, SVG, GML, RSS, MathML etc. For detailed information about XML visit the W3C or read Wikipedia's explanation.