+=head2 WhoBelongToGroups { Groups => ARRAYREF, IncludeSubgroupMembers => 1, IncludeUnprivileged => 0 }
+
+Return members who belong to any of the groups passed in the groups whose IDs
+are included in the Groups arrayref.
+
+If IncludeSubgroupMembers is true (default) then members of any group that's a
+member of one of the passed groups are returned. If it's cleared then only
+direct member users are returned.
+
+If IncludeUnprivileged is false (default) then only privileged members are
+returned; otherwise either privileged or unprivileged group members may be
+returned.