A list of menu objects.
The generic function merge-menu-bars is called by the system to compute the menu bar for a document-frame interface.
The set of visible menus in such an interface is typically made up from those of the frame and those of the active document within it.
There is a built-in unspecialized method that appends the menu bars of the two interfaces and is equivalent to this:
(defmethod capi:merge-menu-bars ((frame t)
You can customize the menu bar by adding methods which specialize on particular frame and document interface classes.
LispWorks CAPI Reference Manual - 21 Dec 2009