Menu: allow mouse hover to open submenu

[mtyson]

Add it as an option for hovering a menu item to open the sub menu, even if the menu/menubar isn't focused.

[mtyson]

Diff to add allowSubmenuHover prop to enable hover popup of submenus.

[bill]

Are you talking about hovering over a MenuBar that isn't focused aka active? I tried pre-1.4, namely ​test_Menu.html in 1.3, and it doesn't open the submenu either: . And ​test_Menu.html in 1.2 doesn't even have a MenuBar.

[bill]

Modified description since it doesn't seem like menus ever worked this way. Maybe back in the 0.4 days?

Note that hovering does open a submenu, but only after the menu itself has gotten focus by clicking it. This is the same way that menus on windows and mac work. But still, I guess it's an understandable enhancement request.

The patch is very small and looks good. Would need to add a test case though.

The main issue I see is with accessibility. Currently, opening a submenu puts focus on (the first item of) the submenu, which seems disruptive, especially if the user was focused somewhere else and was just (for example) sliding the mouse out of the way, and happened to move over a menu.

I think I'd like to have that "focus issue" fixed before adding this feature.

[bill]

In [30900]:

Add passivePopupDelay property to allow menus to open merely by hovering them. Fixes #10979 !strict.