title: Iframe content loading and onload event
body: <p>Having following code</p>
  
  <pre><code>&lt;iframe id="myframe" src="..."&gt;&lt;/iframe&gt;
  
  &lt;script&gt;
  document.getElementById('myframe').onload = function() {
    alert('myframe is loaded');
  };
  &lt;/script&gt;
  </code></pre>
  
  <p>Am I right that the <code>iframe</code> content is loaded by an extra thread so there may be a race condition? Is it possible that the <code>iframe</code> content will be loaded before the event handler in the script (running in the main thread) causing the <code>alert</code> to newer show?</p>