anchor.diff:  ;;    . it should be deactivatable
   
   ;; - the slider needs a total overhaul
  -
  -;; - OPTION-PANE needs an implmentation
   
   ;; - TEXT-FILED, TEXT-AREA dito
   
  
positive.code:                 :documentation "A function to compare two items for equality.")))
  
  (defclass generic-list-pane (list-pane meta-list-pane
                                         value-changed-repaint-mixin
                                         mouse-wheel-scroll-mixin)
    ((highlight-ink :initform +royalblue4+
  
negative.code:         (multiple-value-bind (x0 y0 x1 y1)
              (multiple-value-call #'values
                (transform-position (sheet-delta-transformation parent nil) cx0 cy0)
                (transform-position (sheet-delta-transformation parent nil) cx1 cy1))
            ;; Note: This :suggested-width/height business is really a silly hack
            ;;       which I could have easily worked around without adding kludges
            ;;       to the scroller-pane..
            (let* ((topmost-pane (if scroll-p 
                                    ;list-pane
                                    (scrolling (:scroll-bar :vertical
                                                :suggest-height height   ;; Doesn't appear to be working..
                                                :suggest-width (if scroll-p (+ 30 (bounding-rectangle-width list-pane))))
                                       list-pane)
                                    list-pane))
                   (topmost-pane    (outlining (:thickness 1) topmost-pane))
                   (composed-height (space-requirement-height (compose-space topmost-pane :width (- x1 x0) :height height)))
                   (menu-frame      (make-menu-frame topmost-pane
                                                     :min-width (bounding-rectangle-width parent)
                                                     :left x0
                                                     :top (if (eq position :below)
                                                              y1
                                                              (- y0 composed-height 1)))))
              (values list-pane topmost-pane menu-frame)))))))
  
  (defun popup-list-box (parent)
  