title: Why we need to add <div id="fb-root"></div>
body: <p>Why we need to add these pair of tags within our facebook application. What's the use of this pairs of tags. 
  I created an application which use an apprequest, and it works good even if I didn't add these tags in front of my scripts.
  So I really wonder why we need to add them.
  Thank you.</p>