title: Communicating cross-origin from parent to child iframe
body: <p>I'm working through <a href="//thirdpartyjs.com">Third Party Javascript</a>. I'm particularly interested in communication between a parent page and a child frame from a different origin. Using window.postMessage, it's trivial to safely send messages from the child and have the parent receive them with the <code>message</code> event.</p>
  
  <p>I have had no luck going the other direction. Can I get some confirmation that it is <em>not</em> possible to communicate from the parent to the child using postMessage? If not what are ways of working around this problem? </p>