handle is the %hw - Handle output from a window that has already been created.
If the handle is set to zero then %nw uses the currently active window.
%nw allows you to change the properties of an existing window. In
particular you can use %nw to define or redefine %mn - Menu and %pm - Popup Menu menus on the fly.
This includes %em - Enhanced Menu enhanced menus but not old enhanced menus (%`mn and %`pm).
Alternatively handle could be the handle of a particular control (%lc - Handle of Last Control)
in an existing window (by using winio@ in a %sc - OnShow Callback callback for
example). %nw - Change Window Properties%pm - Popup Menu will then provide a popup menu for the associated control.