anchor.diff:  (defun generic-option-pane-compute-label (pane)
     (generic-option-pane-compute-label-from-value pane (gadget-value pane)))
   
  -(defmethod initialize-instance :after ((object generic-option-pane) &rest rest)
  +(defmethod initialize-instance :after ((object generic-option-pane) &rest rest)  
     (setf (slot-value object 'current-label)
  -        (generic-option-pane-compute-label object)))
  +        (if (slot-boundp object 'value)
  +            (generic-option-pane-compute-label object)
  +            "")))
   
   (defmethod (setf gadget-value) :after (new-value (gadget generic-option-pane) &key &allow-other-keys)
     (setf (slot-value gadget 'current-label)
  
positive.code:               (t (values nil :above height)))))))
  
  (defun popup-init (parent manager frame)
    (let ((list-pane (make-pane-1 manager frame 'generic-list-pane
                                  :items (list-pane-items parent)
                                  :mode  (list-pane-mode parent)
                                  :value (gadget-value parent)
                                  :name-key (list-pane-name-key parent)
                                  :value-key (list-pane-value-key parent)
                                  :test (list-pane-test parent))))
      (multiple-value-bind (scroll-p position height)
          (popup-compute-height parent list-pane)
        (with-bounding-rectangle* (cx0 cy0 cx1 cy1) parent
  
negative.code: 
  (defmethod initialize-instance :after ((gadget meta-list-pane) &rest rest)
    (declare (ignorable rest))
    ;; Initialize slot value if not specified
    #+NIL ;; XXX
    (when (slot-boundp gadget 'value)
      (setf (slot-value gadget 'value)
            (if (list-pane-exclusive-p gadget)
                (funcall (list-pane-value-key gadget) (first (list-pane-items gadget)))
                (mapcar #'list-pane-value-key (list (first (list-pane-items gadget)))))))
      
    (when (and (not (list-pane-exclusive-p gadget))
               (not (listp (gadget-value gadget))))
      (error "A :nonexclusive list-pane cannot be initialized with a value which is not a list."))
  