I remember Android apps some years back that showed an approximate scrollbar, when it knew how many items there were (paragraphs, in the case I’m vaguely recall

I remember Android apps some years back that showed an approximate scrollbar, when it knew how many items there were (paragraphs, in the case I’m vaguely recalling—and although all the content was available, it might not have wanted to render it all at once, as it could have tens of thousands of words) but not how tall each was. I think it drew a scrollbar with the assumption that off-screen items would be a certain height, so if you went from a screenful of long paragraphs to a screenful of short paragraphs the scrollbar could be amusingly wonky, considering our usual expectation of spatial scrollbars. In some contexts this itemwise rather than spatial scrollbar can actually be more useful, but whether or no, it’s not a concept the web supports directly, and there will be certain niggles in the result of implementing it.