[xsl] XSL help

I am new to XSL:key.

Could any one tell for the following,
1) <xsl:variable name="result" select="key($index,$key)"/> what it does
2) To find long descripting, the existing xsl mapping for Type="PP" and
searching keyword for ZZ.  Question: without specifying the attibue name
such as Pkey and Type....How it searching the output of LongDes as ZO
Contracts ???

> From the exising Input xml file,
<Document>
  <Legend>
        <TypeDesc Type="PP" Id="1" PKey="ZZ" xml:lang="EN" ShDes="ZZ"
LongDes="ZO Contracts"/>
  </Legend>
</Document>

Requirement: To find LongDes

Exising XSL file:

<xsl:call-template name="getLegend">
        <xsl:with-param name="cat" select="'PP'"/>
        <xsl:with-param name="key" select="'ZZ'"/>
</xsl:call-template>

<xsl:template name="getLegend">
        <xsl:param name="cat"/>
        <xsl:param name="key"/>
        <xsl:call-template name="lookup">
                <xsl:with-param name="index" select="'legendIndex'"/>
                <xsl:with-param name="key"
select="concat($cat,'_',$key)"/>
                <xsl:with-param name="doc" select="$legend"/>
                <xsl:with-param name="expr" select="'@LongDes'"/>
        </xsl:call-template>
</xsl:template>

<xsl:template name="lookup">
        <!-- index name, i.e. name of the key -->
        <xsl:param name="index"/>
        <xsl:param name="key"/>
        <!-- default value -->
        <xsl:param name="default" select="''"/>
        <!-- node in index source document, per default default value
-->
        <xsl:param name="doc" select="$default"/>
        <!--expr to evaluate to return value, per default result node
-->
        <xsl:param name="expr" select="'.'"/>
        <!-- force context to document where the lookup table is -->
        <xsl:for-each select="$doc[1]">
                <xsl:variable name="result" select="key($index,$key)"/>
                <xsl:choose>
                        <xsl:when test="$result">
                                <xsl:value-of
select="xalan:evaluate(concat('$result[1]/',$expr))"/>
                        </xsl:when>
                        <xsl:when test="$default">
                                <xsl:value-of select="$default"/>
                        </xsl:when>
                </xsl:choose>
        </xsl:for-each>
</xsl:template>

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