title: document.activeElement in iframe shows unspecified error in IE standards mode
body: <pre><code>console.log(document.activeElement);
  </code></pre>
  
  <p>This code is in an iframe, when opening a page which contains this iframe shows "SCRIPT16389: Unspecified error" in IE 8/9 standards mode. No problem when opening in quirks mode. I'm clueless about this, I have searched whether IE supports document.activeElement, its specified as >IE4 is supported.</p>