We have no documentation for HTML attribute completions:

No documentation for HTML attribute value completions either:

As we progress in #62976, these should be implemented so custom tag/attribute providers could offer a good experience.

MDN actually has neat descriptions for all of them:

• https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes
• https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes