[xsl] Trying to match elements NOT found in external document

["G. T. Stresen-Reuter" <tedmasterweb@xxxxxxxxx>]

Hi.

It's been a while since I've written. I hope this email finds everyone  
doing well... on to business...

I'm trying to match items in the source XML document that are NOT  
present in an external XML document.

For example, Given the following XML documents I would like to match  
the atom:entry element whose atom:id = xyz by virtue of the fact that  
there is no corresponding email story with the same id.

feedsource.xml
<atom:feed>
    <atom:entry>
        <atom:id>123</atom:id>
        <atom:title>Story 1</atom:title>
    </atom:entry>
    <atom:entry>
        <atom:id>ABC</atom:id>
        <atom:title>Story 2</atom:title>
    </atom:entry>
    <atom:entry>
        <atom:id>xyz</atom:id>
        <atom:title>Story 3</atom:title>
    </atom:entry>
</atom:feed>

emailedstories.xml
<emails>
    <email>
        <story>
            <id>123</id>
        </story>
        <story>
            <id>ABC</id>
        </story>
    </email>
</emails>

I've tried the following and in spite of the fact that most  
documentation states that keys include documents included via the  
document() function, I've been unable to verify that this is true.  
Here is the stylesheet I've tried to no avail:


<xsl:key name="emailedstories" match="id" use="normalize-space(.)" />

[...]
<!-- there are many references to emailedstories.xml prior to the line  
below, for example -->
<xsl:for-each select="document('../subscriptions/emailedstories.xml')/ 
emails/email">
[...]

<!-- to select just the entry elements that are NOT in the  
emailedstories.xml file, I've been trying this -->
<xsl:apply-templates select="atom:entry[count(key('emailedstories',  
atom:id)) = 0]" />


This doesn't work. I suspect I'm confused about what the context node  
is and/or about comparing node sets vs. strings/numbers.

Does anyone have any suggestions on how to do what I'm trying to do?

Many thanks in advance!

----

G. T. Stresen-Reuter
Web: http://tedmasterweb.com
Blog: http://tecnotertulia.com
Twitter: http://twitter.com/tedmasterweb