Comments

      <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:comment>The first comment</xsl:comment>
                  <bbb>
                        <ccc>
                              <xsl:comment>The second comment</xsl:comment>
                        </ccc>
                  </bbb>
            </xsl:template>

      </xsl:stylesheet>

      <aaa/>

<!--The first comment-->
      <bbb>
            <ccc><!--The second comment--></ccc>
      </bbb>