Should CSS generated contents ::before and ::after really become part of the document?

Hi all,

As you may have heard, assistive technologies are currently regarding CSS
generated contents ::before and ::after as part of the document and are
reading them.

On the contrary, it looks like that web browsers such as Google Chrome and
Firefox aren't regarding ::before and ::after as part of the document
because they are making those contents uncopiable.

Personally, I find this issue quite confusing. Judging from the
presentational nature of CSS, it seems to me that assistive technologies'
behaviors on this matter are not working as intended. But I'm not sure
about that because I can find no official word from W3C on this matter.

I might have missed something. Should CSS generated contents ::before and
::after really become part of the document?

Sincerely,
Ian Yang