Perfect Pangram Perfect Square

Type each letter once.

Controls
Arrow keys to move
X to type a letter
Z to undo
R to reset

This game follows through on a proper puzzle idea based on A Bad Typing Interface.

Confused? This was made as inscrutable trash to be sifted and ciphered through, but if you really want to be directly informed about what’s going on here, and explanation is provided below, encoded with ROT13:

Rnpu yrggre vf n svir-ol-svir fcevgr, naq gurl ner nyy neenatrq va n svir-ol-svir tevq. Gur vavgvny tevq vf zvffvat gur yrggre N, ohg vg vf haqreynvq jvgu “zngf” gung sbez gur fcevgr bs gur yrggre N. Gur phefbe pnaabg geniry orgjrra znggrq naq haznggrq gvyrf. Rnpu gvzr n yrggre vf glcrq, vg orpbzrf gur bar zvffvat yrggre, naq gur zngf ner erneenatrq gb sbez vgf fcevgr. Cerivbhfyl glcrq yrggref (vaqvpngrq va erq) pnaabg or glcrq ntnva.

Source Code