iOS scroll-collapse lab

Open each in turn, swipe up a few times, and watch the green line at the bottom. COLLAPSED +n means Safari's toolbars actually retracted — that is innerHeight growing, which is the only thing the bars are. Every reading is streamed back automatically.

A — plain long page The control. Ordinary paragraphs, nothing clever. If this one does not collapse, nothing else here matters. B — invisible spacer One screen of content plus an empty two-viewport spacer — exactly what the app adds. Does overflow with nothing in it count? C — fixed panel + swipe strip The app's actual shape: a full-screen fixed panel that eats touches, and a 44px strip at the top to start the scroll on. D — inner scroller Expected to fail. It is the check that the instrument can say no.