Missing version in stylesheet

Every xsl:stylesheet element must declare a version attribute to identify the XSLT version the stylesheet conforms to. Omitting it produces an invalid stylesheet that a conformant XSLT processor is required to reject.

Incorrect:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <!-- stylesheet logic -->
</xsl:stylesheet>

Correct:

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
    <!-- stylesheet logic -->
</xsl:stylesheet>