请问之前别人做的XHTML的几个标签及属性含义

    <xhtml:div id="visible-element" style="height:100%;width:100%;overflow: hidden;"> 

      <xsl:if test="/root/flag = 'true'"> <!-- 这个test内容参数/root/flag是哪来的？ -->

        <xhtml:table style="width:100%;overflow: hidden;"> 

          <xsl:for-each select="/root/data/*/tasks/SA_Task">  <!-- 这个select的值是怎么回事？求解释 -->

            <xsl:variable name="onclickvalue">justep.Portal.openWindow('

              <xsl:value-of select="fXM"/>', '

              <xsl:value-of select="$url"/>', '

              <xsl:value-of select="sCreatorFID"/>');

            </xsl:variable>  <!-- $url哪来的?-->

            <tr> 

              <td style="width:12px"/>  

              <td class="className" width="100%"> 

                <nobr> 

                  <a class="className"> 

                    <xsl:attribute name="href">javascript:void(0)</xsl:attribute>  

                    <xsl:attribute name="onclick"> 

                      <xsl:value-of select="$onclickvalue"/> <!-- select值是哪来的 -->[/color]

                    </xsl:attribute>  

                    <xsl:value-of select="fXM"/>