anchor.diff:      WITH = _token('with');
   
       // built-in identifiers
  -
       ABSTRACT = _token('abstract');
       AS = _token('as');
       DYNAMIC = _token('dynamic');
  
positive.code:     _libraries();
    }
  
    /**
     * Defines whitespace, documentation and comments.
     */
    void _whitespace() {
      def('whitespace', whitespace()
        .or(ref('singe-line comment'))
  
negative.code:       .seq(string('*/')));
    }
  
    /** Helper to define a token parser that consumes whitespace. */
    Parser _token(input) {
      var parser = input is Parser ? input :
        input.length == 1 ? char(input) :
  