anchor.diff:    We call that property within our `getHeroes` method when anyone asks for heroes.
   
   //- FIXME refer to Dart API when that page becomes available.
  -- var injMetaUrl = 'https://angular.io/docs/ts/latest/api/core/index/InjectableMetadata-class.html';
  +- var injUrl = 'https://angular.io/docs/ts/latest/api/core/index/Injectable-decorator.html';
   h3#injectable Why @Injectable()?
   :marked
  -  **<a href="#{injMetaUrl}">@Injectable()</a>** marks a class as available to an
  +  **<a href="#{injUrl}">@Injectable()</a>** marks a class as available to an
     injector for instantiation. Generally speaking, an injector will report an
     error when trying to instantiate a class that is not marked as
     `@Injectable()`.
  
positive.code:       for _every class with at least one decorator_.
  
        While any decorator will trigger this effect, mark the service class with the
        <a href="#{injMetaUrl}">InjectableMetadata</a> #{_decorator}
        to make the intent clear.
  
  .callout.is-critical
  
negative.code:   We *can* add it if we really want to. It isn't necessary because the
    `HeroesComponent` is already marked with `@Component`, and this
    !{_decorator} class (like `@Directive` and `@Pipe`, which we'll learn about later)
    is a subtype of <a href="#{injUrl}">Injectable</a>.  It is in
    fact `Injectable` #{_decorator}s that
    identify a class as a target for instantiation by an injector.
  
  +ifDocsFor('ts')
  