Created attachment 384448 [details] Testcase to reproduce the issue Check the attached example and compare the result with Chromium or Firefox. The element "foo" has absolute position and vertical writing mode, in WebKit it's placed outside of the parent element, when in Chromium and Firefox it's placed next to the "Second line".
Created attachment 384449 [details] Rendering in WebKit vs Chromium/Firefox
This might be same issue than bug #189513.
I am unable to reproduce this issue in Safari Technology Preview 152 on macOS 12.5.1 and "foo" is now showing similar to Chrome and Firefox from reference image. Since all browsers are now working similar, I am going to mark this as "RESOLVED CONFIGURATION CHANGED". Thanks!