LGTM3 On Wednesday, July 1, 2026 at 7:58:54 AM UTC-7 Daniel Bratell wrote:
> LGTM2 (since we are catching up, our documentation requirements are > lowered) > > /Daniel > On 2026-07-01 16:39, Yoav Weiss (@Shopify) wrote: > > I'd appreciate an explainer (even an inline one) that explains what this > does and how we expect developers to use it. > > On Monday, June 29, 2026 at 11:24:59 PM UTC+2 Chris Harrelson wrote: > >> LGTM1 >> >> On Fri, Jun 26, 2026 at 5:34 AM Chromestatus < >> [email protected]> 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> >>> >>> *Motivation* >>> slotAssignment is fixed at shadow root creation, so components using >>> manual slot assignment could not adopt declarative shadow DOM. The gap was >>> raised in https://github.com/WICG/webcomponents/issues/967 and >>> specified in the HTML Standard via >>> https://github.com/whatwg/html/pull/12267 . Both Gecko and WebKit have >>> implemented the attribute, so shipping in Chromium completes cross-engine >>> support. This feature is opt-in and the default ("named") is unchanged. >>> >>> *Initial public proposal* >>> *No information provided* >>> >>> *Search tags* >>> shadow <http:///features#tags:shadow>, DOM <http:///features#tags:DOM>, >>> slot <http:///features#tags:slot> >>> >>> *TAG review* >>> *No information provided* >>> >>> *TAG review status* >>> Not applicable >>> >>> *Goals for experimentation* >>> None >>> >>> *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: currently experimental, aiming to enable it by default from >>> M151 and then retained as a kill switch (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*: >>> https://developer.mozilla.org/en-US/docs/Web/API/HTMLTemplateElement/shadowRootSlotAssignment >>> >>> *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? >>> The new behavior is opt-in, the default behavior remains unchanged, and >>> pages that do not use the attribute are unaffected. >>> >>> >>> *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 >>> >>> *Flag name on about://flags* >>> *No information provided* >>> >>> *Finch feature name* >>> ShadowRootSlotAssignment >>> >>> *Rollout plan* >>> Will ship enabled for all users >>> >>> *Requires code in //chrome?* >>> False >>> >>> *Tracking bug* >>> https://issues.chromium.org/issues/493315747 >>> >>> *Estimated milestones* >>> Shipping on desktop 151 >>> Shipping on Android 151 >>> Shipping on WebView 151 >>> >>> *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). >>> *No information provided* >>> >>> *Link to entry on the Chrome Platform Status* >>> https://chromestatus.com/feature/5178682139344896?gate=6073478714359808 >>> >>> This intent message was generated by Chrome Platform Status >>> <https://chromestatus.com>. >>> >> -- >>> You received this message because you are subscribed to the Google >>> Groups "blink-dev" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To view this discussion visit >>> https://groups.google.com/a/chromium.org/d/msgid/blink-dev/6a3e71b6.cff415cc.dde5e.00b1.GAE%40google.com >>> >>> <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/6a3e71b6.cff415cc.dde5e.00b1.GAE%40google.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- > You received this message because you are subscribed to the Google Groups > "blink-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > > To view this discussion visit > https://groups.google.com/a/chromium.org/d/msgid/blink-dev/74d68ddb-b43e-4f45-a484-38e996711d27n%40chromium.org > > <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/74d68ddb-b43e-4f45-a484-38e996711d27n%40chromium.org?utm_medium=email&utm_source=footer> > . > > -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/d4120555-f1a3-47b9-8039-b7904010fd9fn%40chromium.org.
