I think you want

 <xsl:variable name="cnt"as="xs:integer*>
  <xsl:for-each select="$root//*[name() = $nm]">
    <xsl:value-of select="count(.//*)"/>
  </xsl:for-each>
</xsl:sequence>


or
<xsl:variable name="cnt" select="for $x in $root//*[name() = $nm] return count($x//*)"/>

Both untested.

David

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