The result of Membership (∊) says, for each element of the left argument, whether it appears in the right argument.
'rank' ∊ 'array'
1 1 0 0
'rank' ∊ ↑'array' 'shape' 'bound' ⍝ A 3 by 5 table
1 1 1 0
Using Rank we can ask about membership in multiple arrays separately.
'rank' ∊⍤1 ↑'array' 'shape' 'bound'
1 1 0 0
0 1 0 0
0 0 1 0