anchor.diff:    
     Accordingly, dependencies provided in the root `AppComponent` can be injected into *any* component *anywhere* in the application.
     
  -  That isn't always desireable. 
  +  That isn't always desirable. 
     Sometimes we want to restrict service availability to a particular region of the application.
     
     We can limit the scope of an injected service to a *branch* of the application hierarchy
  
positive.code: :marked
    If we comment out the `@Host()` decorator, Angular now walks up the injector ancestor tree 
    until it finds the logger at the `AppComponent` level. The logger logic kicks in and the hero display updates
    with the gratuituous "!!!", indicating that the logger was found.
  figure.image-display
    img(src="/resources/images/cookbooks/dependency-injection/hero-bio-contact-no-host.png" alt="Without @Host") 
  :marked
  
negative.code:   placing it in the `<ng-content>` slot of the `HeroBioComponent` template:
  +makeExample('cb-dependency-injection/ts/app/hero-bio.component.ts','template','app/hero-bio.component.ts (template)')(format='.')
  :marked
    It looks like this, with the hero's telephone number from `HeroContactComponent` projected above the hero description:
  figure.image-display
    img(src="/resources/images/cookbooks/dependency-injection/hero-bio-and-content.png" alt="bio and contact")    
  :marked
  