role="menuitem" does not support aria-expanded in ARIA 1.1, but the authoring practices requires this

[katiehockman]

"A parent menuitem has aria-expanded set to false when its child menu is not visible and set to true when the child menu is visible."
https://www.w3.org/TR/wai-aria-practices/#menu

This would mean that the element with role="menuitem" toggles aria-expanded depending on whether or not the child submenu is open. However, according to ARIA 1.1, aria-expanded is not supported for role="menuitem".

There either needs to be a change to the ARIA 1.1 spec to include aria-expanded as a supported state, or a change to the authoring practices guide (and the associated example that follows this practice).

[mcking65]

the menuitem role supports aria-expanded in ARIA 1.2 with ARIA commit 5bc57d4
and this change is visible in the editor's draft of 1.2.
It is also supported in the current version of the HTML validator.

We previously had notes about validation errors as documented in issue #447, but we have since removed them.