Japanese vertical text is not working on iOS

[chocolatkey]

iOS 27 on iPhone:

ScreenRecording_07-09-2026.01-42-02_1.mp4

While I am aware that vertical-rl support in the ts-toolkit is very minimal, in this particular case, it's completely broken as seen in the screen recording. This was tested using the link https://playground.readium.org/read/kusamakura

[JayPanoz]

Hmmmmm this is legitimately mind-bogglong because the DOM is as expected, you can even see the elements being highlighted on the page using dev tools, but it just refuses to render.

Tried removing styles, to no result.

I'll need to investigate more but that looks related to the awful scroll issues with text not rendering that we already had to handle in the past. The vertical snapper is enforcing a WebKit recalc so that appears to be even more complex to find in the rendering path.

[JayPanoz]

Right so I can reproduce with a minimal case.

bugreport-standalone.html

bugreport-iframe.html

Turns out Webkit on iOS struggles with overflowing iframes, and there is nothing I could find to resolve this specific case, unlike the previous issues we encountered. This is probably why the first resource renders and all the other ones are blank.

The best i can do is open an issue in the Webkit tracker if someone can confirm the test case reproduces the issue.

Tried different things in the snapper itself, nothing works. From what I tested, the only solution that worked was displaying the entire iframe within an overflowable container – which, of course, is quite an impactful change – as the snapper is no longer in charge of position monitoring, etc.