The Menu-Button gadget is available only in Liquid CLIM.
The menu-button gadget provides similar behavior to the toggle-button gadget, except that it is intended for items in menus. The returned value is generally the item chosen from the menu.
arm-callback will be invoked when the menu button becomes armed (such as when the pointer moves into it, or a pointer button is pressed over it). When the menu button is actually activated (by releasing the pointer button over it), value-changed-callback will be invoked. Finally, disarm-callback will be invoked after value-changed-callback , or when the pointer is moved outside of the menu button.
Summary: The class that implements an abstract menu button. It is a subclass of
gadget and labelled-gadget-mixin .
Summary: The class that implements a portable menu button; a subclass of menu-button .
Common Lisp Interface Manager 2.0 User's Guide - 7 Aug 2017