Add a 'cancel' button in an iframed page in a facebook <fb:request-form> that closes a parent popup

Question

This came up for me today and I wanted to share a solution for anyone else with this problem. This is a bit of a hack but as we all know working inside facebook is like that sometimes.

I have an application that lives in an iframe and inside that main iframe I have another iframe. I wanted to add a 'cancel' button to a fb request form that lives in that second iframe that would close a popup window that framed my request form (makes it look purty) that lives on the main iframe.

Here's what I did

<fb:serverfbml>
      <script type="text/fbml">
      <fb:fbml>
<fb:request-form action='<?=$callbackurl?>a_post.php?token=<?=$token?>' method='post' type='My App' content='<?=$content?>' invite='false' style="width:500px">  
      <input type='hidden' name='token' value='<?=$token?>' />
      <fb:request-form-submit uid=<?=$uid?> />
      <input type='button' class='inputbutton' name='cancel' value='Cancel' onclick='document.setLocation("<?=$callbackurl?>/callback_popup.php")'/>
      </fb:request-form>
</fb:fbml>
      </script>
      </fb:serverfbml>

Then create callback_popup.php that has your javascript code in it, which now has the correct context to run. Define closePopup and you are set:

<script type="text/javascript">
<!-- 

parent.parent.closePopup();

-->
</script>