anchor.diff:  (defclass delimiter-lexeme (lisp-lexeme) ())
   (defclass text-lexeme (lisp-lexeme) ())
   (defclass sharpsign-equals-lexeme (lisp-lexeme) ())
  -(defclass sharpsign-sharpsign-lexeme (form-lexeme) ())
  +(defclass sharpsign-sharpsign-form (form-lexeme complete-form-mixin) ())
   (defclass reader-conditional-positive-lexeme (lisp-lexeme) ())
   (defclass reader-conditional-negative-lexeme (lisp-lexeme) ())
   (defclass uninterned-symbol-lexeme (lisp-lexeme) ())
  
positive.code:   (let ((string (form-string syntax (first (children form)))))
      (parse-integer string :start 1 :end (1- (length string)) :radix 10)))
  
  (defmethod extract-label ((syntax lisp-syntax) (form sharpsign-sharpsign-lexeme))
    (let ((string (form-string syntax form)))
      (parse-integer string :start 1 :end (1- (length string)) :radix 10)))
  
  
negative.code:                            &rest args)
    (apply #'register-form-label syntax form args))
  
  (defmethod form-to-object ((syntax lisp-syntax) (form sharpsign-sharpsign-form)
                             &rest args)
    (apply #'label-placeholder syntax form (extract-label syntax form) t args))
  
  