anchor.diff:  	(%view-height (bounding-rectangle-height
   		       (or (pane-viewport stream)
   			   stream)))
  -	(view-height  (bounding-rectangle-height stream)))    
  +	(view-height  (bounding-rectangle-height stream)))
       (with-slots (baseline height vspace) stream
         (multiple-value-bind (cx cy) (stream-cursor-position stream)
   	(setf height (max height (text-style-height (medium-text-style medium) medium)))
  
positive.code:                  ;; Let's prevent infinite recursion if there isn't
                   ;; room for even a single character.
  		 (setq split (max (find-split (- margin cx))
                                    (1+ start)))) 
  		(:scroll
  		 (scroll-horizontal stream width))
  		(:allow)))
  
negative.code:    (x :initform 0 :initarg :x-position)
     (y :initform 0 :initarg :y-position)
     (width :initform 8)
     (appearance :type (member :solid :hollow)
                 :initarg :appearance :initform :hollow
                 :accessor cursor-appearance)
     ;; XXX what does "cursor is active" mean?
  