The full XSL language logically consists of three component languages which are described in three W3C (World Wide Web Consortium) Recommendations:
XPath: XML Path Language--a language for referencing specific parts of an XML document
XSLT: XSL Transformations--a language for describing how to transform one XML document (represented as a tree) into another
XSL: Extensible Stylesheet Language--XSLT plus a description of a set of Formatting Objects and Formatting Properties