anchor.diff:  (defun gadgetp (object)
     (typep object 'gadget))
   
  +(defmethod compose-space ((gadget gadget))
  +  (pane-space-requirement gadget))
  +
   ;;
   ;; gadget's colors
   ;;
  
positive.code: (defclass scroll-bar (value-gadget oriented-gadget-mixin range-gadget-mixin) ()
    (:documentation "The value is a real number"))
  
  (defclass scroll-bar-pane (scroll-bar clim-stream-pane)
    ((drag-callback :initarg :drag-callback
  		  :reader scroll-bar-drag-callback)
     (scroll-to-bottom-callback :initarg :scroll-to-bottom-callback
  
negative.code: (defclass text-editor (text-field) ()
    (:documentation "The value is a string"))
  
  (defclass text-editor-pane (text-editor)
    ((width :type integer
  	  :initarg :width
  	  :reader text-editor-width)
  