title: Angular2 parent -> child -> parent binding
body: <p>I've seen the following piece of code at work - <a href="http://plnkr.co/edit/5z4VEQ?p=preview" rel="nofollow noreferrer">http://plnkr.co/edit/5z4VEQ?p=preview</a></p>
  
  <pre><code>&lt;app-component2 [(value)]="value"&gt;&lt;/app-component2&gt; 
  </code></pre>
  
  <p>You can see that we pass a value to a child component and pass it back to the parent when it changes (onChange will only trigger after you focus out of the input box).</p>
  
  <p>Now this code works even though the "valueChange" event emitter isn't subscribed to anywhere. It will only works if the child component has an event emitter and only if said event emitter is called valueChange.</p>
  
  <p>There's obviously some magic going behind the scenes with Angular automagically connecting value and valueChange but I can't find this in the docs / not sure if this is really a supported feature?</p>