[basex-talk] Index for multiple dbs

Hi all, here a question for the weekend ... ;-)

The following query performs perfectly exploiting the attribute index:

for $d in collection("db") where $d//*:item/@id = '2015000000016940' return $d

Why does this not?

("db") ! (for $d in collection(.) where $d//*:item/@id = '2015000000016940' return $d )

In our use case we'd like to have a list of dbs to query on and the list can grow over time so we would not like to change the code by replicating the queries every time a db is added. What is the way out? Thanks, Marco.