title: What's the difference between the root pane and the top-level container, in Swing?
body: <p>I understand that every top level container has some layers:</p>
  
  <blockquote>
    <p>root pane<br>
    layer pane<br>
    content pane<br>
    glass pane</p>
  </blockquote>
  
  <p>but I don't understand whether the root pane is the top level container itself.</p>
  
  <p>What is the relationship between a pane and a container? In fact, when I return a pane with
  <code>getContentPane()</code>, the object is of type <code>Container</code>!</p>