conditional merge

I am attempting a conditional merge when two elements of different XML
files are the same.
Using the example below obtained from
http://www.dpawson.co.uk/xsl/sect2/merge.html#d154e147

 <xsl:copy-of select="document('a.xml')//id[.=document('b.xml')//id]"/>

I can match elements. However, when I attempt to  do a little more
processing such as is seen below, I fail to get the desired results.  When
the elements match I want it to copy that specific element. However, what I
have causes every element to be copied. Any help would be greatly
appreciated.

  <xsl:template match="l_name">
  <xsl:if test="document('a.xml')//l_name[.=document('b.xml')//_name]">
    <xsl:copy>
      <xsl:copy-of select="@*"/>
      <xsl:apply-templates/>
    </xsl:copy>
  </xsl:if>
  </xsl:template>
  </xsl:stylesheet>


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