Comment 1 for bug 399770

Actually it's undesirable to have both operators in the same precedence for practical reasons: One may want to change the arrangement of *one* these operations (e.g., "<set> contains <element>" and "<super-set> expands <sub-set>", instead of the traditional "<element> in <set>" and "<sub-set> is subset of <super-set>), which wouldn't be possible (it'd be changed in both operations).