anchor.diff:  
     String get basePath => _basePath;
     void set basePath(String bp) {
  -    if (_routes.length > 0) {
  -      throw new _RouterException("Cannot alter basePath after adding routes.");
  +    if (routes.length > 0) {
  +      throw new RouterException("Cannot alter basePath after adding routes.");
       }
       _basePath = bp;
     }
  
positive.code:   }
  }
  
  class _ResourceRoute {
    final ResourcePattern pattern;
    final RequestHandler handler;
  
    _ResourceRoute(this.pattern, this.handler);
  }
  
  class _RouterException implements Exception {
    final String message;
    _RouterException(this.message);
  }
  
negative.code: 
    /// Creates a new [Router].
    Router() {
      routes = [];
      unhandledRequestHandler = _handleUnhandledRequest;
    }
  
  