This priority order can be specified with the priority attributte. : template « XSLT stylesheet « XML Tutorial

1. XML Tutorial
2. XSLT stylesheet
3. template

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="/">
      <xsl:apply-templates select="//CCC"/>
    </xsl:template>
    <xsl:template match="CCC" priority="3">
      <h3 style="color:blue">
        <xsl:value-of select="name()"/>
        <xsl:text> (id=</xsl:text>
        <xsl:value-of select="@id"/>
        <xsl:text>)</xsl:text>
      </h3>
    </xsl:template>
    <xsl:template match="CCC/CCC" priority="4">
      <h2 style="color:red">
        <xsl:value-of select="name()"/>
        <xsl:text> (id=</xsl:text>
        <xsl:value-of select="@id"/>
        <xsl:text>)</xsl:text>
      </h2>
    </xsl:template>
</xsl:stylesheet>

Output:

<?xml version="1.0" encoding="UTF-8"?><h3 style="color:blue">CCC (id=c1)</h3><h2 style="color:red">CCC (id=c2)</h2><h3 style="color:blue">CCC (id=c3)</h3>