Transforming strings to lowercase and uppercase

      <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">
                  <upper>
                        <xsl:value-of  select="upper-case(.)"/>
                  </upper>
                  <lower>
                        <xsl:value-of  select="lower-case(.)"/>
                  </lower>
            </xsl:template>

      </xsl:stylesheet>

      <aaa>Hello, world!</aaa>

      <upper>HELLO, WORLD!</upper>
      <lower>hello, world!</lower>