Document scopedcustomelementregistry and its HTMLElement reflection

[ja-y-son]

MDN URL

https://developer.mozilla.org/en-US/docs/Web/API/CustomElementRegistry

What information is incomplete?

The HTML Standard is adding the scopedcustomelementregistry global content attribute and the reflecting HTMLElement.scopedCustomElementRegistry IDL attribute.

The content attribute affects HTML parser creation: the element and its parsed subtree begin with a null custom element registry so a scoped CustomElementRegistry can claim the subtree later through initialize(). Changing the attribute after element creation does not change the assigned registry. The IDL attribute reflects as a DOMString for future extensibility.

What should be documented?

• The scopedcustomelementregistry global attribute.
• HTMLElement.scopedCustomElementRegistry string reflection.
• Parser-only behavior and the relationship to CustomElementRegistry.initialize().
• Serialization behavior at custom element registry boundaries.
• Browser compatibility once implementations adopt the final specification.

References

• HTML specification PR: Introduce scopedcustomelementregistry global attribute whatwg/html#12000
• DOM infrastructure PR: Introduce keep custom element registry null for elements whatwg/dom#1500
• Web Platform Tests PR: Rename customelementregistry to scopedcustomelementregistry web-platform-tests/wpt#62206

[hamishwillee]

Thanks @ja-y-son. MDN does work when there is an implementation.

For anyone coming here, the links for finding out about those are

• Chromium: https://issues.chromium.org/issues/399124619
• Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1874414 - at least some parts done but all behind pref
• WebKit: https://bugs.webkit.org/show_bug.cgi?id=302970