anchor.diff:  
     > [**Router**](router.html): Navigate from page to page within the client
       application and never leave the browser.
  +    
     > [**路由器**](router.html)：在应用程序客户端的页面间导航，并且不离开浏览器。
   
   block angular-feature-testing
  
positive.code:   
    > [**管道**](pipes.html)：在模板中使用管道转换成用于显示的值，以增强用户体验。例如，`currency`管道表达式：
    
    >
    > > `price | currency:'USD':true`
    >
    
    > It displays a price of 42.33 as `$42.33`.
  
  
negative.code: 
    In brief, you must have previously registered a **provider** of the `HeroService` with the injector.
    A provider is something that can create or return a service, typically the service class itself.
    
    简单点说，我们必须先用注入器（injector）为`HeroService`注册一个**提供商（provider）**。
    提供商用来创建或返回服务，通常就是这个服务类本身（相当于`new HeroService()`）。
  
  block registering-providers
    :marked
      You can register providers in modules or in components.
      
      我们可以在模块中或组件中注册提供商。
      
      In general, add providers to the [root module](#module) so that
      the same instance of a service is available everywhere.
    
      但通常会把提供商添加到[根模块](#module)上，以便在任何地方都使用服务的同一个实例。
    
    +makeExcerpt('src/app/app.module.ts (module providers)', 'providers')
  
  