Sub-query: In
The "in" operator allows you to indicate a condition on members of a saved set or to indicate successive conditions.
Query Path [not] in @Set,MetaClass where Condition
Grouped conditions also allow you to indicate successive conditions, see
Grouped conditions.
Examples:
select Message where Diagram in @Mod
select Message where Source-Org-Unit in @Org-Unit where name like “Department#”