anchor.diff:     (visibility :initform nil
   	       :accessor cursor-visibility)))
   
  -;;; Must be implemented by subclasses of cursor-mixin
  -
   (defgeneric cursor-height (cursor))
   
   (defmethod print-object ((cursor cursor-mixin) stream)
  
positive.code: ;	    do (do-char))))
  
  (defmethod stream-character-width ((stream standard-extended-output-stream) char &key (text-style nil))
    (text-style-character-width (or text-style (medium-text-style (sheet-medium stream)))
  			      (sheet-medium stream)
  			      char))
  
  (defmethod stream-string-width ((stream standard-extended-output-stream) string
  				&key (start 0) (end nil) (text-style nil))
  
negative.code:    )
    )
  
  (defmethod initialize-instance :after ((stream standard-extended-output-stream) &rest args)
    (declare (ignore args))
    (setf (stream-text-cursor stream) (make-instance 'standard-text-cursor :sheet stream)))
  
  (defmethod stream-cursor-position ((stream standard-extended-output-stream))
    (cursor-position (stream-text-cursor stream)))
  
  (defmethod* (setf stream-cursor-position) (x y (stream standard-extended-output-stream))
    (setf (cursor-position (stream-text-cursor stream)) (values x y)))
  