anchor.diff:    It's easy with *!{_Observable}s* as we'll see.
   
     ### Search-by-name
  +
     We're going to add a *hero search* feature to the Tour of Heroes.
     As the user types a name into a search box, we'll make repeated HTTP requests for heroes filtered by that name.
   
  
positive.code:   a#rxjs-imports
    :marked
      ### Import RxJS operators
      Most RxJS operators are not included in Angular's base `Observable` implementation.
      The base implementation includes only what Angular itself requires.
  
  
negative.code:   The `!{_priv}http.get()` call in `HeroSearchService` is similar to the one
    in the `HeroService`, although the URL now has a query string.
  
  +ifDocsFor('ts')
    :marked
      A more important difference: we no longer call `toPromise`.
      Instead we return the *observable* from the the `htttp.get`, 
      after chaining it to another RxJS operator, <code>map</code>, 
      to extract heroes from the response data.
  
      RxJS operator chaining makes response processing easy and readable.
      See the [discuss below about operators](#rxjs-imports).
  
  :marked
    ### HeroSearchComponent
  
    Let's create a new `HeroSearchComponent` that calls this new `HeroSearchService`.
  