Re: [csswg-drafts] [cssom-view] scrollIntoView spec text ("determine the scroll-into-view position") disagrees with browser behavior on which writing-mode(s) to use to determine sides (#11796)

Here's a testcase: https://bug1789464.bmoattachments.org/attachment.cgi?id=9468983

As noted in the testcase: when you click the button to call...
```
  myElem.scrollIntoView({
      behavior: "smooth",
      inline: "center",
      block: "start",
    });
```
... all major browser engines (Chrome 135 dev, Safari 18.3, and Firefox Nightly 137.0a1 (>= 2025-02-27)) interpret "inline" and "block" in terms of the target element, rather than interpreting it in terms of the scroller boxes.

Specifically, browsers scroll both scroll-containers such that the blue box ends up at the left edge and vertically centered in each of the scroll containers.  (And these choices of position come from interpreting the "inline" and "block" options in terms of the target element's writing-mode, rather than the scrollers' writing modes.)

If we instead did what the spec said, we'd instead end up with the blue box vertically-centered and right-aligned in the inner scroller, and then horizontally-centered and top-aligned in the outer scroller -- see my mockup of that in https://bugzilla.mozilla.org/show_bug.cgi?id=1789464 (which is using an earlier version of the testcase so the surrounding content looks a bit different but the idea is the same).

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Received on Thursday, 27 February 2025 17:55:30 UTC