@mcking65
This PR doesn't conflict with #1340 at all because this PR only touches Required Context Role in the Characteristics Tables, and your PR only changes words in the prose. In fact, I think they work together to more strongly clarify how groups fit in to listboxes and trees.

This PR also touches the menuitem roles. After both PRs go in, we can look at whether the menuitem prose needs to be updated to match the new prose in listbox and tree. I'll open an issue as a reminder.

I think we are missing changes to required context role on
row (table -> rowgroup , grid -> rowgroup, treegrid -> rowgroup)

Good catch, @jnurthen !
Agreed, and done.
I have re-requested a review from you. Thanks!

This is ready for final review.

The latest commit reorders group/rowgroup items that are required context roles for option, treeitem, and menuitem roles so that the group comes first, followed by left arrow, followed by the contained item role, as suggested by @jnurthen in today's call.

This uses a left-pointing arrow character in an abbr with title="contained by", which is basically a copy of the markup with the right-pointing arrow character in an abbr with title="containing" that has been used in required owned elements since ARIA 1.0. I've opened #1368 to revisit this markup, as discussed on the call.