XSL is a language for expressing stylesheets. It consists of two parts: a language for transforming XML documents, and an XML vocabulary for specifying formatting semantics. (W3C Recommendation 15 October 2001)
The official XSL Transformations (XSLT) specification. XSLT is a language derived from XSL for transforming XML documents into other XML (or HTML) documents. (W3C Recommendation 16 November 1999)
A schema language for defining the syntactic structure and partial semantics of XML document types; an alternative to XML DTDs. [W3C Note 30 July 1999]
This document proposes a structural schema facility, Document Content Description (DCD), for specifying rules covering the structure and content of XML documents. [W3C Note 31 July 1998]