Navigation menus (drop down / sub menus / fly out etc.) that are either navigable via 1) Arrow Keys or 2) Tab key may or may not convey navigation hints. 

For example: It becomes difficult to follow along with a screen reader in the absence of information on the how to navigate the menu when users are expected to press enter on the main menu followed by tabbing through submenus, or, in the absence of information regarding the complexity, for instance, a menu containing 3 or more sub levels.

Even though “arrow key” navigation is more prevalent whereby certain aria roles would announce navigation hints, in some cases it is still not the case. In those exceptional cases, serving as a fall back option, it would be helpful to hear hints -- for example, inserting a pre-defined custom control (aria?) on the first menu item conveying "navigation hints."

Something on the lines of a hidden table summary attribute, but through attributes that already contain such hints.

Devarshi