XSL Concepts and Practical Use: Transformations

What is an XSL Stylesheet?

XSLT Stylesheets are XML documents; namespaces are used to identify semantically significant elements.
Most stylesheets are stand-alone documents rooted at <xsl:stylesheet> (or <xsl:transform>). It is possible to have "single template" stylesheet/documents.

Note that it is the mapping from namespace abbreviation to URI that is important, not the literal namespace abbreviation "xsl:" that is used most commonly.