anchor.diff:                 :initform *default-text-style*
                  :accessor medium-text-style)
      (default-text-style :initarg :default-text-style
  -     :initform *default-text-style*
  -     :accessor medium-default-text-style)
  +                       :initform *default-text-style*
  +                       :accessor medium-default-text-style)
      (sheet :initarg :sheet
             :initform nil                 ; this means that medium is not linked to a sheet
             :reader medium-sheet
  
positive.code: 
  (defclass standard-line-style (line-style)
    ((unit        :initarg :line-unit
  	        :initform :normal
  	        :reader line-style-unit
                  :type (member :normal :point :coordinate))
     (thickness   :initarg :line-thickness
  	        :initform 1
  	        :reader line-style-thickness
                  :type real)
     (joint-shape :initarg :line-joint-shape
  		:initform :miter
  		:reader line-style-joint-shape
                  :type (member :miter :bevel :round :none))
     (cap-shape   :initarg :line-cap-shape
  	        :initform :butt
  	        :reader line-style-cap-shape
                  :type (member :butt :square :round :no-end-point))
     (dashes      :initarg :line-dashes
  	        :initform nil
  	        :reader line-style-dashes
                  :type (or (member t nil)
                            sequence))))
  
  (defun make-line-style (&key (unit :normal) (thickness 1)
  			     (joint-shape :miter) (cap-shape :butt)
  			     (dashes nil))
    (make-instance 'standard-line-style
      :line-unit unit
      :line-thickness thickness
      :line-joint-shape joint-shape
      :line-cap-shape cap-shape
      :line-dashes dashes))
  
  (defmethod print-object ((self standard-line-style) stream)
    (print-unreadable-object (self stream :type t :identity nil)
  
negative.code:   (let ((old-buffer (gensym)))
      `(let ((,old-buffer (medium-buffering-output-p ,medium)))
         (setf (medium-buffering-output-p ,medium) ,buffer-p)
         (unwind-protect (progn ,@body)
           (setf (medium-buffering-output-p ,medium) ,old-buffer)))))
  
  
  