title: What does require_self mean?
body: <p>In rails3.1 <code>application.css</code> we could see</p>
  
  <pre><code>/*
   *= require_self
   *= require_tree .
  */
  </code></pre>
  
  <p>I know that <code>require_tree .</code> is just telling the system to bundle together everything from the stylesheets folder into a single file.</p>
  
  <p>But what does <code>require_self</code> tells?</p>