title: Can a <hr /> element have a closing tag?
body: <p>My colleague doesn't really know or understand html. Her job is to input information into the CMS and I've noticed she keeps closing her <code>&lt;hr /&gt;</code> tags like this <code>&lt;hr&gt;&lt;/hr&gt;</code>.</p>
  
  <p>I've had a Google but I can't find anywhere that says this isn't allowed or could cause problems. I know it's supposed to be <code>&lt;hr /&gt;</code> but is it worth me telling her or is it unnecessary but valid markup?</p>
  
  <p>NB The doctype for our website is 
  <code>XHTML 1.0 Transitional</code> if that makes any difference.</p>
  
  <p><strong>EDIT</strong></p>
  
  <p>@Jeff had a good idea about validating. I used the following code and apparently this is valid  XHTML 1.0 Transitional</p>
  
  <pre><code>&lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"&gt;
  &lt;html xmlns="http://www.w3.org/1999/xhtml"&gt;
      &lt;head&gt;
          &lt;title&gt;&lt;/title&gt;
      &lt;/head&gt;
      &lt;body&gt;
          &lt;hr&gt;&lt;/hr&gt;
      &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>