↕ — Full windowsS↕Y: full windows of sizes S on leading axes. Trailing axes stay inside each window.
3↕⍳5 ⍝ 3 3⍴1 2 3 2 3 4 3 4 5
2 2↕2 3⍴⍳6 ⍝ 1 2 2 2⍴1 2 4 5 2 3 5 6
2↕3 2⍴⍳6 ⍝ 2 2 2⍴1 2 3 4 3 4 5 6
Shape: position-frame, sizes, trailing axes. Position counts: 0⌈1+((≢S)↑⍴Y)-S.
4↕'ab' ⍝ 0 4⍴' '
0↕'ab' ⍝ 3 0⍴' '
⍬↕2 3⍴⍳6 ⍝ 2 3⍴⍳6
Oversized windows give empty frames. Zero sizes give n+1 empty windows; ⍬ leaves Y unchanged. For padded neighbourhoods, see Stencil.
RANK: sizes not scalar/vector, or too many axes. DOMAIN: negative or non-integral size.