ACTION-2063: Research why it says "user agents might use aria-activedescendant..."

The "might" was changed by me (when I was working on the aria-activedescendant changes) because what is currently in the spec is a non-normative "may". And we all agreed that non-normative "may" SHOULD NOT be used.

I did my best to see when that non-normative "may" got introduced. Some data points:

* It is in https://www.w3.org/TR/2009/WD-wai-aria-20090224
* It is not in https://www.w3.org/TR/2008/WD-wai-aria-20080806
* https://www.w3.org/2008/11/03-pf-minutes has David Bolter raising some issues about focus and tablist
* Also discussed here: https://lists.w3.org/Archives/Member/w3c-wai-pf/2009JanMar/0260.html
* However, the latter seem to be talking about ATs trying to change focus through that property

With the PF actions that are closed having been deleted, and this well preceding our use of github, further research is going to be challenging. I believe I've done due diligence looking for the answer to this question. And I see that Matt resolved the problem in his branch by removing the non-normative "may" and leaving the rest of the text in that statement as-is. Fine by me. :)

Closing this action.