anchor.diff:  ;; (make-opacity 1) = +foreground-ink+ = +everywhere+
   ;;
   ;; --GB
  -
  -;;;; What we may want to have
   
   ;; It might be handy to have the equivalent of parent-relative
   ;; backgrounds. We can specify new indirect inks:
  
positive.code: 
  (defun make-rectangular-tile (design width height)
    (make-instance 'rectangular-tile
      :width width
      :height height
      :design design))
  
  
  ;;;
  
  (defclass in-compositum (design)
    ((ink :initarg :ink :reader compositum-ink)
     (mask :initarg :mask :reader compositum-mask)))
  
  (defmethod print-object ((object in-compositum) stream)
  
negative.code:         (t
           (make-instance 'standard-opacity :value value))))
  
  ;;;;
  ;;;; 13.7 Flipping Ink
  ;;;;
  