Unclear how <td> to <th> association is exposed to accessibility APIs

[zcorpan]

See this twitter thread:
https://twitter.com/aardrian/status/1486108208351621135

When the headers attribute is absent, I don't see text in html-aam that says to expose the cell's assigned headers, for example, in Table.ItemColumnHeaderItems and Table.ItemRowHeaderItems.

When the headers attribute is present, it says to do so, but still doesn't say what the value should be.

In both cases, I would expect to see some kind of reference to the "assigned headers" in step 7 in https://html.spec.whatwg.org/multipage/tables.html#header-and-data-cell-semantics

(Maybe the HTML spec should have a linkable term here?)