[xsl] Xpath conditional

["Joseph L. Casale jcasale@xxxxxxxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

Hi have some XML resembling the following:

<?xml version="1.0" encoding="utf-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi";>
    <Fragment>
        <DirectoryRef Id="WEBSITEDIR">
            <Component Id="cmpCA929998DABB546D9DBF11366AF00C73" Guid="*">
                <File Id="fil621D71236777E77CBCD8796C747EFDFF" KeyPath="yes"
Source="$(var.MyVar)\Global.asax" />
            </Component>
            <Component Id="cmp431AD7A30B0DC39715871007A26AE68B" Guid="*">
                <File Id="fil24F96AF9459A0FF6768697EEBAAA4133" KeyPath="yes"
Source="$(var.MyVar)\load.aspx" />
            </Component>
        </DirectoryRef>
    </Fragment>
    <Fragment>
        <ComponentGroup Id="WebsiteComponents">
            <ComponentRef Id="cmpCA929998DABB546D9DBF11366AF00C73" />
            <ComponentRef Id="cmp431AD7A30B0DC39715871007A26AE68B" />
        </ComponentGroup>
    </Fragment>
</Wix>

How can I generate a match expression for a template that selects
the ComponentRef whose @Id equals the enclosing Component @Id
which wraps a File element with a known @Source.

In this simpler cases, a query predicate that doesn't have the nested
conditional is trivial however in this case I am clear how to write this.

At runtime, I will only know the Fle/@Source value and need to map
this back to a ComponentRef element.

Thakns,
jlc