> <xsl:template match="constraint:*">
> <!-- some code -->
> </xsl:template>
> 
> if I apply my template to the XML file above then it will catch all
> the three elements. is there any way I can find out which one is
> currently being caught by the current template that the program
> counter is in?

See 

  http://www.w3.org/TR/xpath-functions/#func-local-name

<xsl:template match="constraint:*">
  <xsl:variable name="ln" select="local-name(.)"/>
  <xsl:choose>
    <xsl:when test="$ln eq 'SimpleConstraint'">
      ... handle constraint:SimpleConstraint ...
    </xsl:when>
    <xsl:when test="$ln eq 'And'">
      ... handle constraint:And ...
    </xsl:when>
    <xsl:otherwise>
      <!-- otherwise just process the contents -->
      <xsl:copy>
        <xsl:apply-templates select="@*|node()"/>
      </xsl:copy>
    </xsl:otherwise>
  </xsl:choose>
</xsl:template>

> My second question, is there any way I can identify and copy those
> parts of the code that have not been caught by any of the defined XSLT
> template, to the output?

Well, a default template is the way we normally handle that.  At
the top of many stylesheets which are mostly copying the input data
you will find something like this:

  <xsl:template match="@*|node()">
    <xsl:copy>
      <xsl:apply-templates select="@*|node()"/>
    </xsl:copy>
  </xsl:template>

Jim

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James A. Robinson                       jim.robinson@xxxxxxxxxxxx
Stanford University HighWire Press      http://highwire.stanford.edu/
+1 650 7237294 (Work)                   +1 650 7259335 (Fax)