anchor.diff:  
     Shell shell = new Shell();
     shell.startup();
  +
  +  shell.registerComponentObject(tools);
   }
   
   class Tools {
     void startup({String fullScreenButtonSelector: "#full_screen", String consoleSelector: "#console"}) {
       querySelector(fullScreenButtonSelector).onClick.listen((event) => querySelector(consoleSelector).requestFullscreen());
  +  }
  +
  +  String help() {
  +    return "-- help: Print documents";
     }
   }
   
  
positive.code: class Shell {
    final Logger logger = new Logger("Shell");
    DivElement _console;
  
    Shell({String consoleSelector: "#console"}) {
      _console = querySelector(consoleSelector);
  
negative.code: import "dart:html";
  import "dart:mirrors";
  import "dart:math" as math;
  import "package:logging/logging.dart";
  
  void main() {
    Logger.root.level = Level.ALL;
  