title: URL change ajax call in Facebook
body: <p>In facebook, whenever you navigate to a different URL (in some situations), the URL changes but there is no feeling sensed as going to a different page. </p>
  
  <p>For example: when we view pictures in facebook, and when we move to the next image the URL changes in the address bar </p>
  
  <p>FROM >facebook.com/foo?bar=foobar&amp;xxxx=</p>
  
  <p>TO > >>facebook.com/foo?bar=boobar&amp;xxxx=</p>
  
  <p>and this is not hashed change also
  like </p>
  
  <p>FROM >facebook.com/xxxxx#xxx=xxxx</p>
  
  <p>TO > >>facebook.com/xxxxx#xxx=yyyy</p>
  
  <p>How is this possible seamlessly. I mean how is that only a container is modified on URL change. URL change is supposed to navigate to a different page which can contain cached information from previous page and THIS navigation by URL change can be seen obviously by browser's screen going blank for a moment. </p>
  
  <p>If using an iFrame, how to implement this ?</p>