anchor.diff:    
     It is stateful because the pipe maintains a subscription to the input and its returned values depend on that subscription.
   
  -  Here is an example of binding a simple promise to a view, using the async pipe.
  +  In the next example, we bind a simple promise to a view with the async pipe.
   
   code-example(format="linenums").
     @Component({
  
positive.code:     `,
      pipes: [FetchJsonPipe]
    })
    class HeroesList implements AfterViewInit {
    }
  
    bootstrap(HeroesList);
  ```
  
negative.code:   A pipe may accept any number of optional parameters to fine-tune its output.
      
    We add parameters to a pipe by following the pipe name with a colon ( : ) and then the parameter value
    (e.g., `currency:'EUR'`). If our pipe accepts multiple parameters, we separate the values with colons (e.g. `slice:1:5`)
    
    We'll modify our birthday example to give the date pipe a format parameter.
    The formatted date should display as **<span style="font-family:courier">04/15/88</span>**.
  
  code-example(format="linenums" escape="html").
    <p>The hero's birthday is {{ birthday | date:"MM/dd/yy" }} </p>
  