Query referring to multiple schemas

It’s easy to run simple queries on Tamino from XMLSpy. How would you run queries of the following type using XMLSpy:

for $a in input()/a, $b in input()/b
where $a/some_field = $b/another_field
return $a/data

XMLSPY directly support currently only
Tamino X-Query 3 and not Tamino XQuery 4.

However you can use the XMLSPY HTTP mechanism to access Tamino via XQuery 4 e.g.

open url
http://pcwwa2/tamino/welcome_4_2_0/bibc?_XQUERY=for+$i+in+input()/bib return $i