title: how facebook grab link information?
body: <p>when you type a link in facebook you can see the title, site name, description and images of this link. what i know is facebook use two ways to grab link information:</p>
  
  <p>1-using the <code>og</code> tags </p>
  
  <p>2-using the meta tags inside head tag of html.</p>
  
  <p>but there are websites for example don't have any <code>og</code> tags or meta tags about description and facebook display its description and title.</p>
  
  <p>my question, if the website doesn't has any <code>og</code> tags or meta tags, from where it get the description information?</p>
  
  <p>when i post this link for example in a facebook post <code>http://php.net/</code> i can see description appear although i cann't find any <code>og:description</code> tags or any meta tags in the sourse of the page. also if you post the link of this question to facebook you can see the question itself apear, how does facebook do this?</p>