Currently, if you create a menu using MenuAnchor, and you tab to the button, you can activate it, but you can't traverse to the submenu using the keyboard. This is because the submenu is in the overlay, and the button isn't handling the key events.

I'm not quite sure what the fix for this is, because it may be that the button itself has to add a shortcut for the arrow and tab keys to get to the submenu. Or maybe it just needs to focus the first item in the submenu when activated.