anchor.diff:    Earlier we registered the `Logger` service in the `providers` array of the metadata for the `AppComponent` like this:
     
     以前，我们通过`AppComponent`元数据中的`providers`数组注册过`Logger`服务，就像这样：
  +  
   // #enddocregion providers-1
   +makeExample('dependency-injection/ts/app/providers.component.ts','providers-logger')
   // #docregion providers-2
  
positive.code:   If someone extends the `Engine` class, that is not `Car`'s problem.
    
    如果有人扩展了`Engine`类，那就不再是`Car`类的烦恼了。
  // #enddocregion why-4
  // Must copy the following, due to indented +make.
  .l-sub-section
  
negative.code:     We're writing in TypeScript and have followed the parameter name with a type annotation, `:HeroService`.
      The class is also decorated with the `@Component` decorator (scroll up to confirm that fact).
      
      我们利用TypeScript编程，在参数名后面带有一个类型注解：`:HeroService`。
      这个类还有一个`@Component`的装饰器（往上翻翻就知道了）。
  
      When the TypeScript compiler evaluates this class, it sees the `@Component` decorator and adds class metadata
  