anchor.diff:    
     Where did the injector get that value?
     It may already have that value in its internal container. 
  -  It it doesn't, it may be able to make one with the help of a ***provider***.
  +  If it doesn't, it may be able to make one with the help of a ***provider***.
     A *provider* is a recipe for delivering a service associated with a *token*.
   .l-sub-section
     :marked
  
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:   
    Accordingly, dependencies provided in the root `AppComponent` can be injected into *any* component *anywhere* in the application.
    
    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
  