xsl:key, predicates and documents.

Afternoon

I've found myself confused by something I thought that I understood so I'm
hoping for some enlightenment. We have a fairly massive document that
is used as a lookup when processing other documents.

Right now, we have the big document used as the primary input to 
stylesheet and the document actually being processed is loaded via
document(). 

The big document can be partioned on an attribute. The lookups done
in this document depend on the attribute value in both the input and
the lookup. That is, if the @PER attribute is 'n' then we will be
doing lookups based on the @HW attribute and if 'y' on the @SUR attribute.

So, I created keys that look like this:

    <xsl:key name="term-key" select="e[@PER='n']" use="@HW"/>
    <xsl:key name="person-key" select="e[@PER='y']" use="@SUR"/>

    
Our root template matches the other document and processes it so:

<xsl:param name="in-file"/>
<xsl:variable name="in-doc" select="document($infile)"/>
<xsl:template match="/">
    <output>
        <xsl:apply-templates select="$in-doc/xData/eData"/>
    </output>
</xsl:template>

<xsl:template match="eData[@PERS='n']">
    <xsl:variable name="exact" select="key('term-key', @HW)"/>
    ...

</xsl:template>

We know that there are matches yet this doesn't work unless
we remove the predicate from the key definition. Are predicates
usable in key definitions?

On a related noted, is there any way to reverse this so that
the key data is loaded from document()?

cheers

nic