After #1340 and #1359 are merged, need to update the prose for the menuitem roles (i.e. including menuitemcheckbox and menuitemradio) with the new wording from #1340 that better explains how groups can be used with menuitems. See #1359 (comment) for details.

For example, treeitem in #1340 says:

Authors MUST ensure elements with role treeitem are contained in, or owned by, an element with role tree or an element with role group that is contained in, or owned by, an element with role treeitem.