The whiteboard look you asked about — but not the Excalidraw format underneath. The source is the same structured data as v2; the sketchy boxes and arrows are drawn fresh by a 27KB library at load, so a regenerated diagram never needs pixel arithmetic. Same rule: two levels visible, tap a box to step inside.
Boxes with a doorway mark (⌕) open. The caption above the drawing is this page's note handle for anything the sketch itself makes hard to tap.