The Extensible Stylesheet Language (XSL) includes both a transformation language and a formatting language. Each of these, naturally enough, is an XML application. The transformation language provides elements that define rules for how one XML document is transformed into another XML document.
The transformed XML document may use the markup and DTD of the original document, or it may use a completely different set of elements. In particular, it may use the elements defined by the second part of XSL, the formatting objects.