anchor.diff:    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.
   
  
positive.code:   The `!{_priv}http.get()` call in `HeroSearchService` is similar to the one
    in the `HeroService`, although the URL now has a query string.
  
    <span if-docs="ts">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).
    </span>
  
    ### HeroSearchComponent
  
    Let's create a new `HeroSearchComponent` that calls this new `HeroSearchService`.
  
negative.code:   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.
  
  