The generic function redisplay-interface updates the state of an interface, such as enabling and disabling menus, buttons, and so forth, that might have changed since the last call. When using this as a callback, you can use :redisplay-interface instead of the symbol, and then it will get passed the correct arguments regardless of the callback type.
This method is called by popup-confirmer to update its button's enabled state, and so it should be called when state changes in a dialog.
CAPI User Guide and Reference Manual (Unix version) - 25 Feb 2015