[csswg-drafts] [css-view-transitions-2] Cross-document View Transition when there is a UA transition (#8953)

khushalsagar has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-view-transitions-2] Cross-document View Transition when there is a UA transition ==
This is related to https://github.com/w3c/csswg-drafts/issues/8888 but deserves its own discussion/resolution. Also related reading is https://github.com/w3c/csswg-drafts/issues/8747.

A navigation can involve a visual transition from both the UA and the author but we only want one to occur. Ideally author transitions should take precedence but there are cases where that's not possible because the requisite primitives are missing. The swipe scenario described [here](https://github.com/WICG/view-transitions/blob/main/default-ua-transitions.md#transition-cases) is one such case where some browsers (Chrome/Safari on iOS) already do a visual transition. It would be incorrect to do a ViewTransition following the browser transition.

So the UA needs to decide whether to execute the site's custom ViewTransition or override it with a UA transition, which is a tradeoff. For example:

* Chrome/Safari on iOS do a visual transition with the page content during the swipe. The site doing a ViewTransition after this won't make sense.
* Chrome/Firefox on Android don't do any visual transition during the swipe. The site could do a ViewTransition here when the swipe ends (similar to pressing the back button).

While browsers should err on the side of prioritizing the author's ViewTransition over the UA transition, it can be quite limiting for browser UX. This seems like something that could be left to the UA with a recommendation as long as only one transition is executed (avoiding correctness issues). For example, the browser will know whether the site wants to do a ViewTransition when the user starts swiping. It can choose to suppress the UA transition in favour of running the ViewTransition or choose to skip the ViewTransition (as if the author didn't opt-in to ViewTransitions) in favour of running the UA transition.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/8953 using your GitHub account


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Received on Tuesday, 13 June 2023 00:22:53 UTC