anchor.diff:    is to set ARIA attributes, as in this example:
   +makeExample('template-syntax/ts/app/app.component.html', 'attrib-binding-aria')(format=".")
   :marked
  -  ### Class binding
  +  ### Class Binding
   
     We can add and remove CSS class names from an element’s `class` attribute with
     a **class binding**.
  
positive.code: 
    <a id="eventemitter"></a>
    <a id="custom-event"></a>
    ### Custom events with EventEmitter
  
    Directives typically raise custom events with an Angular [EventEmitter](../api/core/index/EventEmitter-class.html).
    A directive creates an `EventEmitter` and exposes it as a property.
  
negative.code: 
  .l-main-section
  :marked
    ## Event Binding
    The bindings we’ve met so far flow data in one direction: *from the component to an element*.
  
    Users don’t just stare at the screen. They enter text into input boxes. They pick items from lists.
  