Concat values

What I am trying to do is based on a value $attrName I need to check
every line item to see if this value exist in that Line Item.  If it
does exist for a particular line item I need to get the value of the
line item and pass it back and concatenate it with a | under a
particular attribute.

Hence I should produce something like this:

ExtendedAttributeDefinitionObjectLink="LineItem1|LineItem2|LineItem3"
...

Where are the Line Item names with a matching $attrName gets appended to
the Attribute above.
 


<xsl:attribute name = "ExtendedAttributeDefinitionObjectLink">
        <xsl:variable name="GroupLineItems" />

        I Loop through the line items here...
        <xsl:for-each
select="../../../../../ListOfRequestQuoteDetails/RequestQuoteDetails">
            <xsl:variable name="LineItem">

        I call the template below looping through the Reference of the
Line Item
                <xsl:apply-templates
select="RequestQuoteItemDetail/BaseItemDetail/ListOfItemReferences/ListO
fReferenceCoded/ReferenceCoded" mode="BidLineItems">

     
        Passing the template the value I have to match on.
                    <xsl:with-param name="fieldName"
select="$attrName"/>
                </xsl:apply-templates>
            </xsl:variable>

        Trying to concatenate... but of course this will not work
            <xsl:variable name="GroupLineItems"
select="concat($LineItem,'|')" />
        </xsl:for-each>
        <xsl:value-of select="$GroupLineItmes" />
</xsl:attribute>

My Template is below

<xsl:template match="ReferenceCoded" mode="BidLineItems">
    <xsl:param name="fieldName"/>
    <xsl:if test="ReferenceTypeCodedOther='QuestBidExtendedAttribute'">
        <xsl:if test="PrimaryReference/Reference/RefNum=$fieldName">
            <xsl:value-of
select="SupportingReference/Reference/RefNum"/>
        </xsl:if>
    </xsl:if>
</xsl:template>

Thanks... James