anchor.diff:  (defmethod compose-space ((pane single-child-composite-pane)
                             &rest args &key width height)
     (declare (ignore width height))
  -  (if (sheet-child pane)
  -      (apply #'compose-space (sheet-child pane) args)
  +  (if-let ((child (sheet-child pane)))
  +      (apply #'compose-space child args)
         (make-space-requirement)))
   
   (defmethod allocate-space ((pane single-child-composite-pane) width height)
  -  (when (sheet-child pane)
  -    (allocate-space (sheet-child pane) width height)))
  +  (when-let ((child (sheet-child pane)))
  +    (allocate-space child width height)))
   
   ;;; TOP-LEVEL-SHEET
   
  
positive.code:           (draw-text* pane (clime:label-pane-label pane)
                        tx ty)
            ;;;
            (when (sheet-children pane)
              (with-drawing-options (pane
                                     :clipping-region
                                     (region-difference
  
negative.code: 
  (defmethod allocate-space ((pane label-pane) width height)
    (multiple-value-bind (right top left bottom) (label-pane-margins pane)
      (alexandria:when-let ((child (sheet-child pane)))
        (multiple-value-bind (x1 y1 x2 y2) (values 0 0 width height)
          (move-sheet child (+ x1 left) (+ y1 top))
          (allocate-space child
  