A component that combines a button or editable field and a drop-down list.
The user can select a value from the drop-down list, which appears at the
user's request.
WingMenu is a component
that can be used as a menu, menu bar and popup menu.
It can be also used as typical component and added to
container like buttons and other dialog fields.
Menu is a list containing WingMenuItems and another WingMenus.