∊ — Enlist / Membership∊Y recursively ravels all nested leaves.
∊(1 2⋄ 3 (4 5)) ⍝ 1 2 3 4 5
X∊Y marks items of X found among the elements of Y, using tolerant matching. A single query returns an atom. Batch axes follow X’s shape.
1 2 3∊2 4 ⍝ 0x 1x 0x
'banana'∊'an' ⍝ 0x 1x 1x 1x 1x 1x
C←'cat' 'dog'
(⊂'dog')∊C ⍝ 1x
(,⊂'dog')∊C ⍝ ,1x