Porthole is a small Javascript library that makes it safe and easy to communicate with cross domain iFrames. Porthole relies on hidden iFrames (later referred to a as proxy) to exchange information. The caller sets a url fragment with the message to pass. The proxy by virtue of being served from the same origin as the callee, invokes a callback method with an event object that contains the message read from the url fragment. The message signaling mechanism is based on a resize event.