anchor.diff:    (if (active cursor)
         (active-ink cursor)
         (inactive-ink cursor)))
  +
  +(defmethod (setf enabled) :after ((new-val null) (cursor drei-cursor))
  +  (clear-output-record cursor))
   
   (defclass point-cursor (drei-cursor)
     ()
  
positive.code:   (mark (view cursor)))
  
  (defmethod enabled ((cursor mark-cursor))
    *show-mark*)
  
  (defgeneric visible-1 (cursor view)
    (:documentation "Is `cursor', associated with `view', visible?
  
negative.code:   (declare (ignore initargs))
    (stream-add-output-record (output-stream object) object))
  
  (defgeneric active (cursor)
    (:documentation "Whether the cursor is active or
  not. An active cursor is drawn using the active ink, and an
  inactive is drawn using the inactive ink. Typically, a cursor
  will be active when the associated Drei view has focus.")
    (:method ((cursor drei-cursor))
      (active (view cursor))))
  
  (defgeneric ink (cursor)
    (:documentation "Return the ink object that should be used for
  