[iOS Safari] Tabbing through fields within iFrames via prev/next/done bar doesn't work

[Louis Van Craen]

When there are multiple iFrames (with differing origin), each containing a unique input field, Safari fails to allow tabbing through the input fields.

This behaviour is broken on both mobile safari (v17.4) and desktop safari (v17.4).

iOS Safari - Current behaviour:
  - Using the prev/next arrows on the software keyboard doesn't change the focus from the current input element

iOS Safari - Expected behaviour:
  - Using the prev/next arrows on the software keyboard focuses the prev/next input element

Desktop Safari - Current behaviour:
  - Using the tab key focuses the iFrame element -- a second tab stroke is needed to focus the input element within the iFrame

Desktop Safari - Expected behaviour:
  - Using the tab key focuses the prev/next input element

The current behaviour can be reproduced using the following:
  - Example: https://mfqzp9.csb.app/
  - Code source: https://codesandbox.io/p/sandbox/iframe-forked-mfqzp9?file=%2Fsrc%2Findex.js

[Radar WebKit Bug Importer]

<rdar://problem/125613616>

[Ahmad Saleem]

@Louis - was this used to work with Safari earlier versions?

[Louis Van Craen]

@Ahmad Saleem, I checked on both mobile and desktop, but I was only able to find a version on desktop that worked last. And that would be desktop safari (v12.1).