≢
≢Y counts major cells: first-axis length, or 1 for a scalar.
≢Y
≢2 3⍴0 ⍝ 2x ≢42 ⍝ 1x ≢⍬ ⍝ 0x
X≢Y negates match.
X≢Y
1≢,1 ⍝ 1x