pane.

a window onto content taller than the room you want to give it: the pane scrolls, not the page. what a section becomes when it would otherwise push everything below it off the end of the document — a growing wall of images, a long log, a list with no natural end. it isn't `shelf` (the horizontal errand: a row of cards you skim, sized by the shelf and paged by arrows) — a pane keeps its content exactly as given and only bounds how much of it you see. the thin scrollbar is on by default and is the affordance, written against a class so it survives an app-wide `*::-webkit-scrollbar { display: none }`; scroll chaining is deliberately left alone so the page keeps moving at the end of the pane; the edge is faded only where the content actually continues, measured with a ResizeObserver, and the pane is a tab stop only while it overflows.