anchor.diff:    .alert.is-important
       :marked
        In Angular, there are two types of modules:
  -     - [Angular modules](#angular-module). 
  +
  +     在Angular里有两种模块：
  +
  +     - [Angular modules](#angular-module).
        See the [Angular Module](/docs/ts/latest/guide/ngmodule.html) chapter for details and examples.
  +
  +     - [Angular 模块](#angular-module).到[Angular Module](/docs/ts/latest/guide/ngmodule.html)章节查看详情和例子。
  +
        - ES2015 modules as described in this section.
  +
  +     - 本节描述的ES2015模块。
   
     :marked
       Angular apps are modular.
  
positive.code: <a id="reactive-forms"></a>
  :marked
    ## Reactive Forms
  .l-sub-section
    :marked
      A technique for building Angular forms through code in a component.
      The alternate technique is [Template-Driven Forms](#template-driven-forms).
  
      When building reactive forms:
      - The "source of truth" is the component. The validation is defined using code in the component.
      - Each control is explicitly created in the component class with `new FormControl()` or with `FormBuilder`.
      - The template input elements do *not* use `ngModel`.
      - The associated Angular directives are all prefixed with `Form` such as `FormGroup`, `FormControl`, and `FormControlName`.
  
      Reactive forms are powerful, flexible, and great for more complex data entry form scenarios, such as dynamic generation
      of form controls.
  
  :marked
    ## Router
  
negative.code: .l-main-section
  :marked
    ## Observable
  
    ## Observable
  .l-sub-section
    :marked
      We can think of an observable as an array whose items arrive asynchronously over time. 
      Observables help us manage asynchronous data, such as data coming from a backend service.
      Observables are used within Angular itself, including Angular's event system and its http client service.
  
      一个`Observable`是一个数组，它包含的元素在一段时间内异步到达。`Observable`帮助我们管理异步数据，比如来自后台服务的数据。
      Angular自身使用了`Observable`，包括Angular的事件系统和它的http客户端服务。
  
      To use observables, Angular uses a third-party library called Reactive Extensions (RxJS).
      Observables are a proposed feature for ES 2016, the next version of JavaScript.
  
      为了利用`Observable`，Angular使用了名为Reactive Extensions (RxJS)的第三方包。
      在下个版本的JavaScript - ES 2016中，`Observable`是建议的功能之一。
  
  :marked
    ## Output
  