Missing scoped custom element registries docs

[captainbrosset]

MDN URL

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

What specific section or headline is this issue about?

Multiple

What information was incorrect, unhelpful, or incomplete?

Scoped custom element registries are very useful for consumers of web components, especially for those who use their own component libraries, or that import 3rd-party libraries.

Today, all components are registered into a single, global registry, which means that two different components can't use the same tagname (like <fancy-button>) without the page breaking.

Scoped custom element registries allow consumers to scope different custom elements to different documents, elements, or shadow roots.

This is useful, for example, when importing a 3rd-party component library, or when testing multiple versions of the same library side by side.

The scoped custom element registry feature is documented partially on MDN:

• Existing docs:
  • CustomElementRegistry() constructor, to create a new registry.
  • initialize() method, to scope an element, shadow root, or document to a registry.
  • shadowrootcustomelementregistry attribute, for scoping a registry to a declarative shadow DOM.
  • customElementRegistry property on DOM elements, documents, and shadow roots, to check which registry is a thing associated to.

The following docs (at least) seem to be missing:

• Missing docs:
  • The customElementRegistry option for the attachShadow() method: https://developer.mozilla.org/en-US/docs/Web/API/Element/attachShadow does not mention it
    • From @hamishwillee - will be added by Element.attachShadow() - doc for options.customElementRegistry #43593
  • The customElementRegistry option for the document.createElement() method: https://developer.mozilla.org/en-US/docs/Web/API/Document/createElement#options does not mention it.
    • From @hamishwillee - was added in Ff149 allow more chars in attributes/element names #43350

What did you expect to see?

Adequate docs for the missing pieces listed above.

Do you have any supporting links, references, or citations?

No response

Do you have anything more you want to share?

I think scoped custom element registries are already supported in Safari, and coming to Edge and Chrome 146. Not sure when individual pieces of the API shipped.

[hamishwillee]

@captainbrosset I merged a PR two days ago that might address this - I expect from your list above that these bits were omitted but just in case there was some crossover can you please check #43149

FYI @pepelsbey

[hamishwillee]

@captainbrosset Perhaps also createCustomElementNS() since that allows you to specify the scope as an option.customElementRegistry. I added this in #43350 (comment) but it may be that we also need an update to Web_components/Using_custom_elements#scoped_custom_element_registries since it isn't mentioned there.