public bool prefers_app_menu ()
Determines if the desktop environment in which the application is running would prefer an application menu be shown.
If this function returns true then the application should call set_app_menu with the contents of an application menu, which will be shown by the desktop environment. If it returns false then you should consider using an alternate approach, such as a menubar.
The value returned by this function is purely advisory and you are free to ignore it. If you call set_app_menu even if the desktop environment doesn't support app menus, then a fallback will be provided.
Applications are similarly free not to set an app menu even if the desktop environment wants to show one. In that case, a fallback will also be created by the desktop environment (GNOME, for example, uses a menu with only a "Quit" item in it).
The value returned by this function never changes. Once it returns a particular value, it is guaranteed to always return the same value.
You may only call this function after the application has been registered and after the base startup handler has run. You're most likely to want to use this from your own startup handler. It may also make sense to consult this function while constructing UI (in activate, open or an action activation handler) in order to determine if you should show a gear menu or not.
This function will return false on Mac OS and a default app menu will be created automatically with the "usual" contents of that menu typical to most Mac OS applications. If you call set_app_menu anyway, then this menu will be replaced with your own.
true if you should set an app menu