class ScrollPosition

Where a ScrollView is — for an app that has to remember it and put it back: a folder list returning to the row it was opened from, or a tab whose list should not come back scrolled to where another tab left it.

A reference the app keeps, one per place it wants remembered, and not a binding: the offset is the renderer's and changes every frame of a scroll, and an observed value would rebuild the app's body on each of them. offset follows the renderer without anyone being told. scroll(to:) puts the view there after the next layout — once the content's new length is known, so an offset saved in a long folder is not clamped against the short one being left — and before a lazy list decides which rows to mount, so the first frame there is already full. It jumps rather than eases: the point is to be where you were, not to be seen travelling there.

Handing a ScrollView a different position puts it where that one was.