last() function is in for-each element. The context is therefore all selected chapters. : last « XSLT stylesheet « XML Tutorial

1. XML Tutorial
2. XSLT stylesheet
3. last

File: Data.xml
<?xml version="1.0" encoding="utf-8"?>
<data>
    <chapter>Chapter A</chapter>
    <chapter>Chapter B</chapter>
    <chapter>Chapter C</chapter>
    <chapter>Chapter D</chapter>
</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>
        <xsl:for-each select="//chapter">
          <TR>
            <TD>
              <xsl:value-of select="."/>
              <xsl:text>(last = </xsl:text>
              <xsl:value-of select="last()"/>
              <xsl:text>)</xsl:text>
            </TD>
          </TR>
        </xsl:for-each>
      </TABLE>
    </xsl:template>
</xsl:stylesheet>

Output:

<?xml version="1.0" encoding="UTF-8"?><TABLE><TR><TD>Chapter A(last = 4)</TD></TR><TR><TD>Chapter B(last = 4)</TD></TR><TR><TD>Chapter C(last = 4)</TD></TR><TR><TD>Chapter D(last = 4)</TD></TR></TABLE>