title: List of distinct XML element names using BeautifulSoup
body: <p>I am using BeautifulSoup to parse an XML document. Is there a straight-forward way to get a list of distinct element names that are used in the document?</p>
  
  <p>For example, if this is the document:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;note&gt;
      &lt;to&gt; Tove&lt;/to&gt;
      &lt;from&gt;Jani&lt;/from&gt;
      &lt;heading&gt;Reminder&lt;/heading&gt;
      &lt;body&gt;Don't forget me this weekend!&lt;/body&gt;
  &lt;/note&gt;
  </code></pre>
  
  <p>I would like to get:
  note, to, from, heading, body</p>