title: Do HTML5 elements "work" in non-HTML5 doctypes?
body: <p>I did some internship at a company for re-newing their website. The "problem" was that they are still using a 4.01 doc type, so I hadn't had the chance to get some nice HTML5 going, I thought. But then I saw that some one else implemented a responsive menu with the <code>&lt;nav&gt;</code> tag and it worked. I am confused:</p>
  
  <ul>
  <li>What exactly does the (HTML5) doctype do?</li>
  <li>If HTML5 elements are displayed correctly in HTML4, what is the difference between the two then?</li>
  </ul>