[Popup] Compatibility issue with existing <popup> use

[tomayac]

The UA stylesheet changes introduced in crbug.com/1168738#c6 seem to cause compatibility issues with prior use of <popup>. While this is self-inflicted and was predicted (see @annevk's comment [I know this was written in the context of CE and the present issue is not about a CE]), it may seem nevertheless worthwhile to explore how much of a compatibility issue this is, especially since the Intent to Prototype message mentioned there were no compatibility issues.

[pepelsbey]

Some real life examples:

Reported by developers who (despite of Angular’s recommendations to prefix components) used <popup> element as is.

[gregwhitworth]

Interesting - @mfreed7 @melanierichards either of you want to do some compat analysis?

[melanierichards]

Saw this on Twitter while out of office (thanks again folks for filing)...maybe we should hold on a compat analysis until we have a better idea on names for this element are reasonably in scope. Un-prefixed components might pose a problem with any name that is natural to reach for; it'll likely come up again with other new elements; and I don't think we should hold back the platform for improperly named custom elements. This issue is precisely why the author requirement for a hyphen exists. :) But if there's 2-3 names that seem reasonable and one of these minimizes conflicts with un-prefixed custom elements, maybe that's our winner.

Also, for awareness: https://bugs.chromium.org/p/chromium/issues/detail?id=1168738#c28

[mfreed7]

This is an interesting issue. I agree that I completely missed this potential issue in my intent to prototype. It seems that the compat concerns aren't awful, as there have only been a handful of bugs reported, and most were quickly resolved on the site-side by renaming the element. But it would definitely be good to do this analysis in advance of actually shipping either <popup> or <selectmenu> to the web platform.

@melanierichards thanks for linking that commit. That was in response to this bug: https://crbug.com/1199964. When I added <popup> to the codebase behind a flag, I didn't prevent the UA stylesheet from doing a display:none !important for closed popups, which hid any non-standard <popup> elements a site used. This has been fixed now in Chromium M91, but not in (already stable) M90.

[github-actions]

There hasn't been any discussion on this issue for a while, so we're marking it as stale. If you choose to kick off the discussion again, we'll remove the 'stale' label.

[mfreed7]

Since we're not doing a new element for popup, I think we can just close this.