anchor.diff:  
   (defclass bounding-rectangle () ())
   
  -(defclass region (#|ink|#) ())
  +(defclass region (design) ())
   (defclass path (region bounding-rectangle) ())
   (defclass area (region bounding-rectangle) ())
   (defclass region-set  (region bounding-rectangle) ())
  
positive.code: ;;; --------------------------------------------------------------------------------------
  ;;;  2001-01-21  GB     fixed bug in (TRANSFORM-REGION T RECTANGLE-SET)
  ;;;                     added some documentation
  
  ;;; ---- TODO ----------------------------------------------------------------------------
  
  
negative.code:         radius-2-dx (coerce radius-2-dx 'coordinate)
          radius-2-dy (coerce radius-2-dy 'coordinate)
          start-angle (and start-angle (coerce start-angle 'coordinate))
          end-angle (and end-angle (coerce end-angle 'coordinate)) )
  
    (let ((tr (make-3-point-transformation* 0 0 1 0 0 1
                                            center-x center-y
  