Description
The current spec text for block-ellipsis (which is one of the longhands for line-clamp) says that when an ellipsis is inserted on the last line before clamp, it must be placed after the last soft wrap opportunity that would make the line with the ellipsis not overflow, considering that the content after the ellipsis gets pushed to the next line box or fragment.
However, according to the Unicode line breaking algorithm, ASCII spaces don't have a break opportunity before them, but only after them. Which means any soft wrap opportunity caused by a space would show the ellipsis after the space, not at the end of the word. Or at least that would be the case if the ellipsis inline is added at the end of the line box during line breaking and before phase II of whitespace processing.
There's also the fact that the block-ellipsis spec text allows inserting the ellipsis in the middle of text-wrap: nowrap text, since it only talks about finding the last soft wrap opportunity, and nowrap does not remove wrap opportunities, it just prevents wrapping. Given that, the question comes up of how trailing whitespace would work before the ellipsis inside white-space: pre text. If we just say to collapse as usual according to phase II, and then add the ellipsis, we would still have spaces between the end of the word and the ellipsis in white-space: pre text. Do we want that?