[Webkit-unassigned] [Bug 258282] REGRESSION (264594 at main): Broke custom element built-in polyfill by making form properties non deletable

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=258282

--- Comment #15 from Chris Dumez <cdumez at apple.com> ---
I wrote this very reduced test case which tries to delete property 0 of a form:
https://codepen.io/cdumez/pen/JjeKgLa

Safari before 264594 at main: Able to delete the property
Safari after 264594 at main: Not able to delete the property
Chrome 114: Not able to delete the property
Firefox 114: Not able to delete the property

So it seems like 264594 at main fixed a bug and aligned our behavior with Chrome & Firefox. Unfortunately, it also seems that the custom-elements polyfill was relying on said bug.

At this point, I think the best we could do is detect the policy and maybe quirk our behavior. I think this would also mean detecting the polyfill version so that we can have our new/standard behavior when using the fixed version of the polyfill.

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