This seems like this should be an Intent to Ship, as you're adding
support for a few feature. Is there any reason you chose PSA?
On 6/10/26 12:17 p.m., Chromestatus wrote:
*Contact emails*
[email protected]
*Specification*
https://html.spec.whatwg.org/#attr-template-shadowrootslotassignment
*Summary*
Adds the shadowrootslotassignment attribute to the <template> element,
allowing declarative shadow roots to use manual slot assignment. Until
now this option was only available imperatively, via
attachShadow({slotAssignment: "manual"}), so components that rely on
manual assignment could not create their shadow roots declaratively.
The attribute accepts "named" (the default, preserving current
behavior) and "manual", and is reflected by the
shadowRootSlotAssignment property on HTMLTemplateElement.
*Blink component*
Blink>DOM>ShadowDOM
<https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3EDOM%3EShadowDOM%22>
*Web Feature ID*
declarative-shadow-dom
<https://webstatus.dev/features/declarative-shadow-dom>
*Risks*
*Interoperability and Compatibility*
Low risk. The new behavior is opt-in: it only applies when a page
explicitly sets shadowrootslotassignment="manual", and the default
("named") matches current behavior, so existing content is unaffected.
The attribute is specified in the HTML Standard (merged via
https://github.com/whatwg/html/pull/12267, originally raised in
https://github.com/WICG/webcomponents/issues/967) and both Gecko and
WebKit have already implemented it, so shipping in Chromium completes
cross-engine support. The change is guarded by the
ShadowRootSlotAssignment feature flag (enabled by default from M151),
retained as a kill switch and expected to be removed around M153.
/Gecko/:
Shipped/Shipping (https://bugzilla.mozilla.org/show_bug.cgi?id=2023824)
/WebKit/:
Shipped/Shipping (https://bugs.webkit.org/show_bug.cgi?id=310090)
https://github.com/WebKit/standards-positions/issues/631
/Web developers/:
Positive (https://github.com/WICG/webcomponents/issues/967)
/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 new DevTools work required. The attribute is visible in the
Elements panel like the other shadowroot* attributes, and the
resulting shadow root's mode is already exposed via
ShadowRoot.slotAssignment.
*Will this feature be supported on all six Blink platforms (Windows,
Mac, Linux, ChromeOS, Android, and Android WebView)?*
Yes
*Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?*
Yes
https://wpt.fyi/results/shadow-dom/declarative/declarative-shadow-dom-repeats-slot-assignment.html
https://wpt.fyi/results/shadow-dom/declarative/declarative-shadow-dom-slot-assignment.html
https://wpt.fyi/results/shadow-dom/declarative/declarative-shadow-dom-slot-assignment-serialization.html
*Tracking bug*
https://issues.chromium.org/issues/493315747
*Estimated milestones*
Shipping on desktop 151
Shipping on Android 151
Shipping on WebView 151
*Link to entry on the Chrome Platform Status*
https://chromestatus.com/feature/5203283359694848
This intent message was generated by Chrome Platform Status
<https://chromestatus.com>.
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