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:    (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?
  
negative.code: 				   string
                                     nil
  				   start split)
  	      (setq cx (+ cx width))
            (with-slots (x y) (stream-text-cursor stream)
                  (setf x cx y cy)))
  	    (when (/= split end)
  