function postMessageProtocol(/*string*/ url) {
   // Step 1
   url += '#oslc-postMessage-1.0';
   
   // Step 2
   var frame;
   var listener = function(e) {
      var HEADER = "oslc-response:";
      if (e.source == frame.contentWindow && e.data.indexOf(HEADER) == 0) {
         // Step 4
         window.removeEventListener('message', listener, false);
         destroyFrame(frame);
         handleMessage(e.data.substr(HEADER.length));
      }
   };
   window.addEventListener('message', listener, false);
   
   // Step 3
   frame = doc.createElement('iframe');
   frame.src = url;
   displayFrame(frame);
}