anchor.diff:  
     .l-sub-section
       :marked
  -      The [switchMap operator](https://github.com/Reactive-Extensions/RxJS/blob/master/doc/api/core/operators/flatmaplatest.md)
  +      The [switchMap operator](http://www.learnrxjs.io/operators/transformation/switchmap.html)
         (formerly known as "flatMapLatest") is very clever.
   
  -      Every qualifying key event can trigger an http call.
  -      Even with a 300ms pause between requests, we could have multiple http requests in flight
  +      Every qualifying key event can trigger an `http` method call.
  +      Even with a 300ms pause between requests, we could have multiple HTTP requests in flight
         and they may not return in the order sent.
   
         `switchMap` preserves the original request order while returning
  -       only the observable from the most recent http call.
  +       only the observable from the most recent `http` method call.
         Results from prior calls are canceled and discarded.
   
  -      We also short-circuit the http call and return an observable containing an empty array
  +      We also short-circuit the `http` method call and return an observable containing an empty array
         if the search text is empty.
   
  -      Note that _canceling_ the `HeroSearchService` observable won't actually abort a pending http request
  +      Note that _canceling_ the `HeroSearchService` observable won't actually abort a pending HTTP request
         until the service supports that feature, a topic for another day.
         We are content for now to discard unwanted results.
     :marked
  
positive.code:   :marked
      ### Extracting the data in the *then* callback
  
      In the *promise*'s `then` callback we call the `json` method of the http `Response` to extract the
      data within the response.
    +makeExcerpt('app/hero.service.ts', 'to-data', '')
  
  
negative.code: h1 Providing HTTP Services
  block http-library
    :marked
      The `HttpModule` is ***not*** a core Angular module.
      It's Angular's optional approach to web access and it exists as a separate add-on module called `@angular/http`,
      shipped in a separate script file as part of the Angular npm package.
  
      Fortunately we're ready to import from `@angular/http` because `systemjs.config` configured *SystemJS* to load that library when we need it.
  
  :marked
    ### Register for HTTP services
  
  block http-providers
    :marked
      Our app will depend upon the Angular `http` service which itself depends upon other supporting services.
      The `HttpModule` from `@angular/http` library holds providers for a complete set of HTTP services.
  
      We should be able to access these services from anywhere in the application.
      So we register them all by adding `HttpModule` to the `imports` list of the `AppModule` where we
      bootstrap the application and its root `AppComponent`.
  
    +makeExample('app/app.module.ts', 'v1','app/app.module.ts (v1)')
  