anchor.diff:  (grammar-rule syntax-abstract
     "see 4.2"
     (grammar-and syntax-rule
  -               (grammar-* 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');")
  
positive.code: (grammar-rule terminal-string
    "see 4.16"
    (grammar-or
     (grammar-and first-quote-symbol
                  first-terminal-character
                  (grammar-* first-terminal-character)
                  first-quote-symbol)
     (grammar-and second-quote-symbol
                  second-terminal-character
                  (grammar-* second-terminal-character)
                  second-quote-symbol)))
  
  (grammar-rule gap-free-symbol
    "see 6.3"
  
negative.code: ;;; Abstract EBNF syntax
  ;;;
  
  ;; Suppress warning
  (declaim (ftype function definitions-list))
  
  (grammar-rule optional-sequence
    "see 4.11"
  