title: using html tags in xml document with namespace
body: <p>I want to display a simple line in my <code>xml</code> document using <code>html</code> namespace and tag <code>hr</code></p>
  
  <pre><code>&lt;?xml version="1.0"?&gt;
  &lt;documents xmlns:html="http://www.w3.org/1999/xhtml"&gt;
  &lt;document&gt;
      &lt;title&gt;doc1&lt;/title&gt;
      &lt;html:hr&gt;&lt;/html:hr&gt;
      &lt;text&gt;data1&lt;/text&gt;
  &lt;/document&gt;
  &lt;document&gt;
      &lt;title&gt;doc2&lt;/title&gt;
      &lt;text&gt;data2&lt;/text&gt;
  &lt;/document&gt;
  &lt;/documents&gt;
  </code></pre>
  
  <p>But it shows document in browser like simple xml without any lines but with <code>&lt;html:hr /&gt;</code> instead of line.</p>
  
  <p>What's the problem? </p>