XSLT

XSLT is the eXtended Stylesheet Language Transformations,

a language for transforming XML documents into other XML documents.

XSLT is used to manipulate XML documents into other forms: a sort of glue between data formats. It can turn an XML document into an XHTML document, or even an HTML document. With a little bit of hackery, it can even be convinced to spit out non-XML conforming documents.