title: websites urls without file extension?
body: <p>When I look at Amazon.com and I see their URL for pages, it does not have <code>.htm</code>, <code>.html</code> or <code>.php</code> at the end of the URL.</p>
  
  <p>It is like:<br>
  <a href="http://www.amazon.com/books-used-books-textbooks/b/ref=topnav_storetab_b?ie=UTF8&amp;node=283155" rel="noreferrer">http://www.amazon.com/books-used-books-textbooks/b/ref=topnav_storetab_b?ie=UTF8&amp;node=283155</a></p>
  
  <p>Why and how? What kind of extension is that?</p>