Getting length of a string with string-length() function

      <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">
                  <xxx>
                        <xsl:value-of  select="string-length('Brr')"/>
                  </xxx>
                  <yyy>
                        <xsl:value-of  select="string-length(bbb)"/>
                  </yyy>
                  <zzz>
                        <xsl:value-of  select="string-length(ccc)"/>
                  </zzz>
            </xsl:template>

      </xsl:stylesheet>

      <aaa>
            <bbb>12345</bbb>
            <ccc/>
      </aaa>

      <xxx>3</xxx>
      <yyy>5</yyy>
      <zzz>0</zzz>