Scoped Custom Element Registries

[keithamus]

こんにちは TAG-さん!

I'm requesting a TAG review of Scoped Custom Element Registries.

This is a proposal allows for multiple custom element definitions for a single tag name to exist within a page. This is accomplished by allowing user code to create multiple custom element registries and associate them with shadow roots that function as scopes for element creation and custom element definitions. Potentially custom elements created within a scope use the registry for that scope to perform upgrades. Changes to Document, Element, ShadowRoot, and HTMLTemplateElement APIs provide the surface area of this feature.

• Explainer¹: Mostly in https://github.com/WICG/webcomponents/blob/gh-pages/proposals/Scoped-Custom-Element-Registries.md but with design changes mentioned in Revamped Scoped Custom Element Registries whatwg/html#10854
• Specification: Add Scoped Custom Element Registries whatwg/dom#1341 & Add Scoped Custom Element Registries whatwg/html#10869
• WPT Tests: https://wpt.fyi/results/custom-elements/revamped-scoped-registry?label=master&label=experimental&aligned
• User research: This is driven by the Web Components user community group (via WICG).
• Security and Privacy self-review²: Pending
• GitHub repo: https://github.com/WICG/webcomponents/
• Primary contacts:
  • Anne van Kesteren (@annevk), Apple, specification author, implementer
  • Ryosuke Niwa (@rniwa), Apple, implementer
• Organization/project driving the specification: Apple
• Multi-stakeholder support³:
  • Chromium comments: Positive, worked on the initial prototype (/cc @mfreed7)
  • Mozilla comments: Scoped Custom Elements Registries mozilla/standards-positions#424
  • WebKit comments: Scoped Custom Element Registries WebKit/standards-positions#38
• Status/issue trackers for implementations⁴:
  • Chrome: https://issues.chromium.org/issues/40826514
  • Mozilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1874414
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=267454

Further details:

• I have reviewed the TAG's Web Platform Design Principles
• Previous early design review, if any: N/A
• Relevant time constraints or deadlines: WebKit seems to have a complete implementation and so may well be shipping soon.
• The group where the work on this specification is currently being done: WHATWG
• The group where standardization of this work is intended to be done (if different from the current group):
• Major unresolved issues with or opposition to this specification: I don't think there are any.
• This work is being funded by: Apple