anchor.diff:          ;; avoid going into an infinite loop by not using (setf sheet-region)
           (setf (slot-value pane 'region)
   	      (make-bounding-rectangle 0 0 width height))
  -        (invalidate-cached-regions pane)
  -        #+nil
  -        (allocate-space pane width height)
           (when (or (/= width  old-width)
                     (/= height old-height))
  -          ; is what is called, so we need to check the top level sheet's requirements...
  -          ; (compose-space (first (sheet-children pane)))
  +          (invalidate-cached-regions pane)
             (allocate-space pane width height))))))
   
   (defmethod handle-event ((pane top-level-sheet-pane)
  
positive.code:   (declare (ignore width height))
    (or (pane-space-requirement pane)
        (setf (pane-space-requirement pane)
          (call-next-method))))
  
  (defmethod change-space-requirements ((pane layout-protocol-mixin)
                                        &rest space-req-keys &key resize-frame
  
negative.code: 
        (dada ((foo width height))
              ;; the user wins on the "primary" dimensions
              (when user-foo
                (setf foo (spacing-value-to-device-units pane user-foo)))
              ;;
  