anchor.diff:  ;; MENU-BUTTON gadget
   ;;
   
  -(defclass menu-button (value-gadget labelled-gadget-mixin)
  +(defclass menu-button (labelled-gadget-mixin value-gadget)
     ()
     (:documentation "The value is a button"))
   
  
positive.code: (defun gadgetp (object)
    (typep object 'gadget))
  
  (defmethod compose-space ((gadget gadget))
    (pane-space-requirement gadget))
  
  ;;
  ;; gadget's colors
  ;;
  
negative.code:   (window-clear pane)
    (dispatch-repaint pane (sheet-region pane)))
  
  (defmethod compose-space ((pane text-field-pane))
    (with-sheet-medium (medium pane)
      (multiple-value-bind (width height)
  	(text-size medium (gadget-value pane))
        (make-space-requirement :width width :height height
  			      :max-width width :max-height height
  			      :min-width width :min-height height))))
  
  ;;
  ;; TEXT-EDITOR gadget
  ;;
  