anchor.diff:    :marked
       ### The *PipeTransform* Interface
   
  -    The `transform` method is essential to a pipe. 
  +    The `transform` method is essential to a pipe.
       The `PipeTransform` *interface* defines that method and guides both tooling and the compiler.
       It is technically optional; Angular looks for and executes the `transform` method regardless.
  -    
  +
   :marked
     Now we need a component to demonstrate our pipe.
   +makeExample('pipes/ts/app/power-booster.component.ts',null,'app/power-booster.component.ts')(format='.')
  
positive.code: :marked
    The parameter value can be any valid
    [template expression](./template-syntax.html#template-expressions)
    such as a string literal or a component property. 
    In other words, we can control the format through a binding the same way we control the birthday value through a binding.
    
    Let's write a second component that *binds* the pipe's format parameter
    to the component's `format` property. Here's the template for that component:
  +makeExample('pipes/ts/app/hero-birthday2.component.ts', 'template', 'app/hero-birthday2.component.ts (template)')(format=".")
  
negative.code:   The companion component class provides heroes, pushes new heroes into the array, and can reset the array.
  +makeExample('pipes/ts/app/flying-heroes.component.ts', 'v1', 'app/flying-heroes.component.ts (v1)')(format='.')
  :marked
    We can add a new hero and Angular updates the display when we do.
    The `reset` button replaces `heroes` with a new array of the original heroes and Angular updates the display when we do.
    If we added the ability to remove or change a hero, Angular would detect those changes too and update the display again.
    add or remove heroes. It updates the display when we modify a hero.
  
    ### Flying Heroes pipe
    Let's add a `FlyingHeroesPipe` to the `*ngFor` repeater that filters the list of heroes to just those heroes who can fly.
  +makeExample('pipes/ts/app/flying-heroes.component.html', 'template-flying-heroes', 'app/flying-heroes.component.html (flyers)')(format='.')
  :marked
  