XQuery: no index rewriting

[ChristianGruen]

The following query is not rewritten to utilize the value index. This is probably because the database path information cannot be bound during Expr.compile, but only during Expr.optimize:

let $db := 'factbook'
for $city in db:open($db)//city
where $city/name = 'Berlin'
return $city

[ChristianGruen]

Non-trivial; closed.