anchor.diff:      :initform nil
       :reader prompt-window-history)))
   
  -(defclass prompt-window (floating-window prompt-parameters)
  +(defclass floating-prompt-window (floating-window prompt-parameters)
     ((start-point
       :accessor prompt-window-start-charpos))
     (:default-initargs
  
positive.code: (defun make-prompt-window (buffer parameters)
    (destructuring-bind (x y width height)
        (compute-window-rectangle buffer)
      (make-instance 'prompt-window
                     :buffer buffer
                     :x x
                     :y y
  
negative.code:                    :called-window (prompt-window-called-window parameters)
                     :history (prompt-window-history parameters))))
  
  (defmethod lem::update-prompt-window ((window floating-prompt-window))
    (destructuring-bind (x y width height)
        (compute-window-rectangle (window-buffer window))
      (unless (and (= x (window-x window))
  