title: OnPlatform tags not working in Xamarin Forms
body: <p>I'm using Xamarin Studio 6.1, recently upgraded it to work with a Xamarin Forms project. I can't seem to get the OnPlatform tags working. I'm trying something like this </p>
  
  <pre><code>&lt;Grid Padding="12"&gt;
      &lt;Grid.HeightRequest&gt;
          &lt;OnPlatform /&gt;
      &lt;/Grid.HeightRequest&gt;
  &lt;/Grid&gt;
  </code></pre>
  
  <p>The previewer immediately breaks and complains Invalid XAML: Type <code>OnPlatform not found in xmlns="http://xamarin.com/schemas/2014/forms"</code></p>
  
  <p>I've never seen this error before and can't find any help online. Any ideas?</p>