title: how to use the ref.view-model feature
body: <p>I'm seeing this feature in the docs, but I can't quite figure out how to use it from that information.</p>
  
  <p>It says:
  <code>
  &lt;i-produce-a-value ref.view-model="producer"&gt;&lt;/i-produce-a-value&gt;
  &lt;i-consume-a-value input.bind="producer.output"&gt;&lt;/i-consume-a-value&gt;
  </code>
  What does this look like in real world example?</p>