XSLT Style Sheet Structure (Webmaster in a Nutshell, 3rd Edition)

10.6. XSLT Style Sheet Structure

The general order for elements in an XSL style sheet is as follows:

<xsl:stylesheet version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
   <xsl:import/>
   <xsl:include/>
   <xsl:strip-space/>
   <xsl:preserve-space/>
   <xsl:output/>
   <xsl:key/>
   <xsl:decimal-format/>
   <xsl:namespace-alias/>
   <xsl:attribute-set>...</xsl:attribute-set>
   <xsl:variable>...</xsl:variable>
   <xsl:param>...</xsl:param>

   <xsl:template match="...">
      ...
   </xsl:template>

   <xsl:template name="...">
      ...
   </xsl:template>

</xsl:stylesheet>

Essentially, this ordering boils down to a few simple rules. First, all XSL stylesheets must be well-formed XML documents, and each <XSL> element must use the namespace specified by the xmlns declaration in the <stylesheet> element (commonly xsl:). Second, all XSL stylesheets must begin with the XSL root element tag, <xsl:stylesheet>, and close with the corresponding tag, </xsl:stylesheet>. Within the opening tag, the XSL namespace must be defined:

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

After the root element, you can import external stylesheets with <xsl:import> elements, which must always be first within the <xsl:stylesheet> element. Any other elements can then be used in any order and in multiple occurrences if needed.