anchor.diff:    ### 应用路由
   
   +makeExample('ngmodule/ts/src/app/app-routing.module.ts', '', 'src/app/app-routing.module.ts')(format='.')
  +
   :marked
     The router is the subject of the [Routing & Navigation](router.html) page, so this section skips many of the details and
     concentrates on the intersection of NgModules and routing.
  
positive.code:   对`AppModule`进行适度的修改：
  
  +makeExample('ngmodule/ts/src/app/app.module.3.ts', '', 'src/app/app.module.ts (v3)')
  .l-sub-section
    :marked
      Some file names bear a `.3` extension that indicates
  
negative.code: 
      创建`src/app/core`文件夹
  
    1. Move the `UserService` and `TitleComponent` from `src/app/` to `src/app/core`.
  
      把`UserService`和`TitleComponent`从`src/app`移到`src/app/core`中
      
    1. Create a `CoreModule` class to own the core material.
  
      创建`CoreModule`类来管理这些核心素材
  
    1. Update the `AppRoot` module to  import `CoreModule`.
    
      修改`AppRoot`模块，使其导入`CoreModule`模块
  
  