anchor.diff:    )
   
   ;;???
  +#+NIL
   (defmethod change-space-requirements ((pane pane) &rest rest)
     (declare (ignore rest))
     (values))
   
   ;;???
  +#+NIL
   (defmethod note-space-requirements-changed (sheet (pane pane))
     (declare (ignore sheet))
     (setf (pane-space-requirement pane) nil)
     (compose-space pane)
  -  (if (or (top-level-sheet-pane-p pane) 
  +  (if (or (top-level-sheet-pane-p pane)
   	  (restraining-pane-p pane)
  -	  (and (slot-value pane 'sr-width) 
  +	  (and (slot-value pane 'sr-width)
   	       (slot-value pane 'sr-height)))
         (allocate-space pane (sr-width pane) (sr-height pane))
         (note-space-requirements-changed (sheet-parent pane) pane)))
  
positive.code:     (setf (pane-space-requirement pane)
        (compose-space pane)))
    (when (first (sheet-children pane))
      (allocate-space 
          (first (sheet-children pane))
  	(clamp width (sr-min-width pane) (sr-max-width pane))
  	(clamp height (sr-min-height pane) (sr-max-height pane)))))
  
negative.code:                            (/ user-width 2) (/ user-height 2)
                             (- width user-width)
                             (- height user-height))))
  
  ;;; OUTLINED-PANE
  
  ;; same as SPACING-PANE but a different default background.
  