anchor.diff:  
     The `onKey()` component method is where we extract the user's input
     from the event object, adding that input to the list of user data that we're accumulating in the component's `values` property.
  -  We then use interpolation <!-- PENDING: link to ./template-syntax.html#interpolation) -->
  +  We then use [interpolation](./template-syntax.html#interpolation)
     to display the accumulating `values` property back on screen.
   
     Enter the letters "abc", and then backspace to remove them.
  
positive.code:   which we pass to the component's `onKey()` method.
    The user data we want is in that variable somewhere.
  
  important
  .callout.is-important
    header $event vs. \$event
    :marked
  
negative.code: :marked
    The `(click)` to the left of the equal sign identifies the button's click event as the **target of the binding**.
    The text within quotes on the right is the **template statement** in which we
    respond to the click event by calling the component's `onClickMe` method. A [template statement](./template-syntax.html#template-statements) is a subset
    of Dart with restrictions and a few added tricks.
  
    When writing a binding we must be aware of a template statement's **execution context**.
  