anchor.diff:      Most RxJS operators are not included in Angular's base `Observable` implementation.
       The base implementation includes only what Angular itself requires.
   
  -    大部分RxJS操作符不包括在Angular的`Observable`基本实现中，基本实现中只包括了Angular本身所需的功能。
  +    大部分RxJS操作符都不包括在Angular的`Observable`基本实现中，基本实现只包括Angular本身所需的功能。
   
       If we want more RxJS features, we have to extend  `Observable` by *importing* the libraries in which they are defined.
       Here are all the RxJS imports _this_ component needs:
   
  -    如果想要更多的RxJS功能，我们必须通过*导入*其所定义的库来扩展`Observable`对象，
  -    以下是_这个_模块所需导入的所有RxJS操作：
  +    如果想要更多的RxJS功能，我们必须*导入*其所定义的库来扩展`Observable`对象，
  +    以下是*这个*模块所需导入的所有RxJS操作符：
   
     +makeExample('src/app/hero-search.component.ts','rxjs-imports','src/app/hero-search.component.ts (rxjs imports)')(format='.')
   
  
positive.code:     after chaining it to another RxJS operator, <code>map</code>, 
      to extract heroes from the response data.
  
      更重要的不同：我们不再调用`toPromise`方法，而是从`http.get`
      方法中返回一个*Observable*对象，之后链式调用RxJS操作<code>map</code>
      来从返回数据中提取英雄。
  
      RxJS operator chaining makes response processing easy and readable.
  
negative.code:   We still return a !{_Promise} from both methods. 
    We won't have to update any of the components that call them.
  
    尽管我们在`getHeroes()`和`getHero()`方法的*内部*做了重大修改，
    但是他们的公共签名却没有变。这两个方法仍然返回的是一个!{Promise}对象，
    所以并不需要修改任何调用他们的组件。
  
    Our stakeholders are thrilled with the web API integration so far.
    Now they want the ability to create and delete heroes.
  