Every stylesheet has the following high level structure:

 
<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">


</xsl:stylesheet>

This basic structure defines the document as an xml based document, sets the stylesheet to a version 1.0 stylesheet (ties into the XPath Version and XQuery Version) and defines one of the default namespace for most of the functions.

In this case the “xsl” based functions are validated to the www.w3.org functions.