The Menubar class is a direct descendant of Basecomponent. MenuBar does not add new attributes, but adds a method:
openMenu(menuRef, open)
Opens or closes the specified menu. The open argument is a boolean. A value of true opens the menu, a value of false closes it.
To create a Menubar and add it to the application, you just need to nest the menubar tag within the canvas tag:
<canvas> <menubar> add menus here </menubar> </canvas>