Variables

      <xsl:stylesheet
                  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                  version="2.0">
            <xsl:output  method="xml"
                        indent="yes"
                        omit-xml-declaration="yes"/>

            <xsl:template  match="/aaa">
                  <xsl:variable  name="xxx">A</xsl:variable>
                  <xxx>
                        <xsl:value-of  select="$xxx"/>
                  </xxx>
            </xsl:template>

      </xsl:stylesheet>

      <aaa/>

      <xxx>A</xxx>