Web-Facing Change PSA: Fix mouse focus for slotted elements in Shadow DOM
Di Zhang
Specificationhttps://dom.spec.whatwg.org/#concept-event-dispatch
Summary
Currently, mouse-triggered event will traverse up to the parent or shadow host to find fallback element to receive mouse focus. This doesn't work for slotted content, where we expect the fallback element to receive focus to be the assigned slot, instead of its parent. This is fixed by changing that step to traverse the Flat Tree.
Blink componentBlink>DOM>ShadowDOM
TAG reviewNone
TAG review statusNot applicable
Risks
Interoperability and Compatibility
WPT test: shadow-dom/focus/click-focus-slot-ancestor.html
Gecko: Shipped/Shipping
WebKit: Shipped/Shipping (https://bugs.webkit.org/show_bug.cgi?id=191694)
Web developers: No signals
Other signals:
Ergonomics
There are no ergonomic risk. This feature will fix which element will receive mouse focus for the specific case of a slotted content that cannot be mouse focused. It should not affect performance.
Activation
No, it will be enabled by default. There should be no polyfill necessary as this change should make Blink more interoperable with the other browsers.
Security
N/A. There are no security risk as it does not change whether an element can be focused. It changes the target of a mouse event fallback parent to match web standards and other browsers.
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?
None
Debuggability
N/A. The same DevTools for mouse event handling and focus are applicable for this feature.
Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)?Yes
This feature is for all platforms that uses HTML Shadow DOM and mouse click focus.
Is this feature fully tested by web-platform-tests?Yes
Flag name on about://flagsMouseFocusFlatTreeParent
Finch feature nameNone
Non-finch justification
This is a bug fix.
Requires code in //chrome?False
Tracking bughttps://issues.chromium.org/issues/41420461
Sample links
https://codepen.io/JanMiksovsky/pen/OBjzeY?editors=1000#0
Estimated milestones
Shipping on desktop
133
Shipping on Android
133
Shipping on WebView
133
Anticipated spec changes
Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way).
NoneLink to entry on the Chrome Platform Statushttps://chromestatus.com/feature/5203351732748288?gate=5069763519447040