preceding axis contains all nodes that come before the context node in document order, excluding nodes in the ancestoraxis and attribute and namespace nodes. : proceding « XPath « XML Tutorial

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File: Data.xml
<?xml version="1.0" encoding="utf-8"?>
<data>
    <AAA id="a1" pos="start">
      <BBB id="b1"/>
      <BBB id="b2"/>
    </AAA>
    <AAA id="a2">
      <BBB id="b3"/>
      <BBB id="b4"/>
      <CCC id="c1">
        <CCC id="c2"/>
      </CCC>
      <BBB id="b5">
        <CCC id="c3"/>
      </BBB>
    </AAA>
</data>
File: Transform.xslt

<?xml version="1.0" encoding="utf-8"?>
<xsl:stylesheet
      version="1.0"
      xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/">
      <table border="1" cellpadding="6">
        <tr>
          <th colspan="2">Axis: preceding</th>
        </tr>
        <tr>
          <td>Element</th>
          <td>Node-set</th>
        </tr>
        <xsl:for-each select="/source//*">
          <xsl:call-template name="print"/>
        </xsl:for-each>
      </table>
    </xsl:template>
    <xsl:template name="print">
      <tr>
        <td>
          <xsl:value-of select="name()"/>
          <xsl:text> id = </xsl:text>
          <xsl:value-of select="./@id"/>
        </td>
        <td>
          <xsl:for-each select="preceding::*">
            <xsl:if test="not(@id)">
              <xsl:value-of select="name()"/>
            </xsl:if>
            <xsl:value-of select="./@id"/>
            <xsl:text/>
          </xsl:for-each>
        </td>
      </tr>
    </xsl:template>
</xsl:stylesheet>

Output:

<?xml version="1.0" encoding="UTF-8"?><table border="1" cellpadding="6"><tr><th colspan="2">Axis: preceding</th></tr><tr><td>Element</th><td>Node-set</th></tr></table>