I am unsure about a sentence in the document, so making an issue to inquire further:

In general, the accessibility tree is a simplified version of the DOM in that only information needed by AT is exposed. For example, a span with no semantic information will not be part of the accessibility tree.

I made a document containing two unmarked spans, and am seeing both Firefox and Chrome include them in the AT tree. See screenshot at the bottom.

I also enabled chrome's Screen Reader (which is the only app i have succeeded with using on linux) and it spoke both spans by default.

So what exactly does "not be part of" mean in the sentence?