Html: Shadow DOM and semantic HTML

[hadriann]

This is a request for clarification regarding the use of main element and of h1-h6 elements inside a Shadow DOM, specifically:

1. A non-hidden main element is defined as being unique in a document. In this respect, can each Shadow DOM be considered a separate document? If the Shadow DOM of two web components each contain a main element, can the web components be used in the same document?

2. If the Shadow DOM of a web component contains the title of a page (h1 element and possibly other widgets) and each section of that page is placed in another web component containing the section title (h2 and related text), is this a correct way to mark up the heading relationships of the page? In other words, is it permitted to respect the hierarchy of headings in different (but related) web components?

[annevk]

This needs clarification in the standard I think, but given how AT operates on the flat tree you have to assume that roles (and aria-level, if applicable) are global. More features might be warranted here in due course, but that's a separate discussion.

So 1 is no and 2 is yes, afaik.

cc @whatwg/a11y