anchor.diff:      (sheet-adopt-child instance header)
       (setf (sheet-enabled-p header) t)))
   
  -;;;;
  -;;;; End of original MGR source code
  -;;;;
  -
   (defmethod compose-space ((pane tab-layout-pane) &key width height)
     (declare (ignore width height))
     (let ((q (compose-space (tab-layout-header-pane pane))))
  
positive.code: 
  (defmethod internal-child-p (child (parent tab-layout-pane))
    (eq child (tab-layout-header-pane parent)))
  
negative.code:     (when page
  	(setf (sheet-enabled-p (tab-page-pane page)) t)))
    (call-next-method))
  
  (defclass tab-bar-view (gadget-view)
    ())
  