Koji, as we talked could you take a look at how Scroll anchoring is done and tell us what you think about the following questions in a RTL and vertical mode context:
  - Can Scroll anchoring make the user experience worse in a RTL or Vertical mode context (e.g. wrong or unnecessary reflow mitigation)?


Source code main location:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp

I will take a look at the list of sites you shared with me.
Thanks!

By looking at the code very quickly, we probably want to prioritize TopRight over TopLeft if dir=rtl or writing-mode: vertical-rl. vertical-lr is ok to keep TopLeft.

But even without that, I don't think the feature can make experience worse, just may not improve in some situations.

Thanks for such a quick response, highly appreciated!
If you find anything else, don't hesitate.

The following page seems like a decent test case (images with no dimensions causing reflows):
 - http://peaceroad.github.io/css-layout/vertical/

The intervention seems to work fine (devtools' GPRS connection, scroll to the left OR find in page for a phrase further downstream).

I think this is probably lower priority / non blocking v1.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d91478719a0603374c12efbd79d9cd248770e7ad

commit d91478719a0603374c12efbd79d9cd248770e7ad
Author: ymalik <ymalik@chromium.org>
Date: Tue May 10 23:43:01 2016

Always anchor to top of the anchor element

Anchoring to the bottom corner results in unnecessary adjustment content
is inserted above the anchor position but within the viewport. Always
anchoring to the top has the problem that we wont adjust when content is
inserted below the anchor position but above the viewport. The latter (not
anchoring at all) is better than anchoring to the wrong position.

This CL anchors to the top left for ltr and vertical-lr writing mode and top
right for rtl and vertical-rl writing mode.

BUG= 600891 , 594877 

Review-Url: https://codereview.chromium.org/1958973004
Cr-Commit-Position: refs/heads/master@{#392774}

[modify] https://crrev.com/d91478719a0603374c12efbd79d9cd248770e7ad/third_party/WebKit/Source/core/layout/ScrollAnchor.cpp
[modify] https://crrev.com/d91478719a0603374c12efbd79d9cd248770e7ad/third_party/WebKit/Source/core/layout/ScrollAnchor.h
[modify] https://crrev.com/d91478719a0603374c12efbd79d9cd248770e7ad/third_party/WebKit/Source/core/layout/ScrollAnchorTest.cpp