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:   the component's `onSave()` method whenever a click occurs:
  +makeExample('template-syntax/ts/app/app.component.html', 'event-binding-1')(format=".")
  :marked
    ### Target event
    A **name between enclosing parentheses** &mdash; for example, `(click)` &mdash;
    identifies the target event. In the following example, the target is the button’s click event.
  +makeExample('template-syntax/ts/app/app.component.html', 'event-binding-1')(format=".")
  
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.
  