title: Parsing dtd file with lxml library (python)
body: <p>I need your help.
  I use lxml library to parsing dtd file.</p>
  
  <p>How can i get c subexpression in this example?</p>
  
  <pre><code>dtd = etree.DTD(StringIO('&lt;!ELEMENT a (b,c,d)&gt;'))
  </code></pre>
  
  <p>I try this</p>
  
  <pre><code>content = dtd.elements()[0].content
  
  left, right = content.left, content.right
  </code></pre>
  
  <p>but it left of right subexpression.</p>
  
  <p><a href="http://lxml.de/validation.html#id1" rel="nofollow">http://lxml.de/validation.html#id1</a></p>