anchor.diff:  (defgeneric destroy-mirror (port mirrored-sheet))
   (defgeneric raise-mirror (port sheet))
   (defgeneric bury-mirror (port sheet))
  -(defgeneric port (object))
   
   ;; 9.4.2 Internal Interfaces for Native Coordinates
   
  
positive.code:   (funcall continuation sheet))
  
  
  
  
negative.code: 
  (defgeneric transform-region (transformation region))
  
  ;;;; 8.3.4 Associating a Medium with a Sheet
  
  ;;;; 8.3.4.1 Grafting and Degrafting of Mediums
  
  ;; with-sheet-medium (medium sheet) &body body [Macro]
  ;; with-sheet-medium-bound (sheet medium) &body body [Macro]
  
  (defgeneric sheet-medium (sheet)) 
  (defgeneric medium-sheet (medium)) 
  (defgeneric medium-drawable (medium)) 
  (defgeneric port (medium))
  
  ;;;; 8.3.4.1 Grafting and Degrafting of Mediums
  
  (defgeneric allocate-medium (port sheet))
  (defgeneric deallocate-medium (port medium))
  