title: What variations of WWW part from the URL's host name exist?
body: <p>Most URLs on the web can begin with the <code>www.</code> part:</p>
  
  <blockquote>
    <p><a href="http://www.example.com" rel="nofollow">http://www.example.com</a></p>
  </blockquote>
  
  <p>or without it:</p>
  
  <blockquote>
    <p><a href="http://example.com" rel="nofollow">http://example.com</a></p>
  </blockquote>
  
  <p>But I remember I came across seeing something like this:</p>
  
  <blockquote>
    <p><a href="http://www2.example.com" rel="nofollow">http://www2.example.com</a></p>
  </blockquote>
  
  <p>I need to know what types of the <code>www</code> part of the URL exist besides the ones that I listed above?</p>