Web-Facing Change PSA: User action pseudo class top layer boundary

[Mason Freed]

Contact emails

mas...@chromium.org

Specification

https://www.w3.org/TR/selectors-4/#useraction-pseudos

Summary

This feature represents the behavior described in this section of the CSS spec: https://www.w3.org/TR/selectors-4/#useraction-pseudos which says that :hover, :active, and :focus-within match on the parents of elements, but only up to the first top layer element in the parent chain. The change for Chromium is that last "up to the top layer" part of this behavior. Concretely, this means that for this structure: ``` <main> <div popover> <button></button> </div> </main> <script>document.querySelector('[popover]').showPopover();</script> ``` if the user hovers the `<button>`, then the `:hover` pseudo class will match the `<button>`, and the popover, but will not match the `<main>` element. The rationale behind this change is that typically top layer elements are rendered "elsewhere", in a location that is disconnected from the parent element visually. So it typically does not make sense to change the styles of the parent element when the top layer element is hovered or activated, for example. The customizable-<select> implementation shipped in Chromium has this logic hard-coded for the specific case of the select `::picker()` popover. That special case logic will be removed when this feature ships.

Blink component

Blink>CSS

Web Feature ID

user-action-pseudos

Search tags

top layer, popover

Risks

Interoperability and Compatibility

While this is a behavioral change, in that the user action pseudos will no longer match across top layer boundaries, it is very unlikely to cause compat issues, because the old behavior was so broken. It is unlikely that a site is relying on that behavior intentionally. While it's possible they unintentionally did so, but in that case, this feature will effectively be a bug fix for those sites.

Gecko: No signal

WebKit: No signal

Web developers: No signals

Other signals:

WebView application risks

Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications?

No information provided

Debuggability

No information provided

Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?

No

Is this feature fully tested by web-platform-tests?

No

Tracking bug

https://crbug.com/407769114

Estimated milestones

Shipping on desktop	149
DevTrial on desktop	148
Shipping on Android	149
DevTrial on Android	148
Shipping on WebView	149

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/6296574159355904

This intent message was generated by Chrome Platform Status.