Root element can be either 'stylesheet' or 'transform'.
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> ... </xsl:stylesheet>
<xsl:transform version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> ... </xsl:transform>
The namespace for XSLT is:
http://www.w3.org/1999/XSL/Transform
The version attribute specifies the XSLT version 1.0, 1.1 and 2.0.