anchor.diff:    (grammar-and start-group-symbol
                  definitions-list
                  end-group-symbol))
  -
  -(unintern 'definitions-list) ; end suppress warning
   
   (grammar-rule empty-sequence
     "see 4.14"
  
positive.code: ;;; Abstract EBNF syntax
  ;;;
  
  (defun definitions-list () nil) ; Suppress warning
  
  (grammar-rule optional-sequence
    "see 4.11"
  
negative.code: (grammar-rule syntax-abstract
    "see 4.2"
    (grammar-and syntax-rule
                 (grammar-* syntax-rule)))
  
  ;; Demos
  ;(iso14977:syntax-abstract "test='ab c',\"g\'night\"|'c','d';")
  ;(iso14977:syntax-abstract "test='a b','c d'|3*('e','f');")
  