xpath across 2 documents

[Olivier . Brand]

I have acknowledged that a query across collection does not work.
Can we query on 2 documents at once with XPath ?

example:

users.xml:

<users>
    <user id="1">
     <group id="1"/>
   </user>
<users>

groups.xml:

<groups>
     <group id="1"/>
</groups>


If I want to query all the users who are registred in a group, what should
I write, the following does not work:

/users/[EMAIL PROTECTED] = /groups/[EMAIL PROTECTED]

Is it something possible ?

If not should I just create one big document containing the "users" and
"groups" element ?

Olivier