title: XPath: Select from non-root node fails
body: <p>I'm trying to select nodes starting from nodes that are not root nodes of XML documents. The code the following:</p>
  
  <pre><code> foreach (XmlNode xmlIter in root.SelectNodes("/refentry/refsect1[@id='parameters']/variablelist/*")) {
      Parameter p = new Parameter();
  
      xmlNode = xmlIter.SelectSingleNode("varlistentry/term/parameter");
      p.Identifier = xmlNode.InnerText;
  
      xmlNode = xmlIter.SelectSingleNode("varlistentry/listitem");
      p.Documentation = xmlNode.InnerText;
  }
  </code></pre>
  
  <p>The XML document (here is only a snippet) is the following:</p>
  
  <pre><code>&lt;refsect1 id="parameters"&gt;&lt;title&gt;Parameters&lt;/title&gt;
      &lt;variablelist&gt;
      &lt;varlistentry&gt;
          &lt;term&gt;&lt;parameter&gt;pipeline&lt;/parameter&gt;&lt;/term&gt;
          &lt;listitem&gt;
          &lt;para&gt;
  
          &lt;/para&gt;
          &lt;/listitem&gt;
      &lt;/varlistentry&gt;
      &lt;varlistentry&gt;
          &lt;term&gt;&lt;parameter&gt;program&lt;/parameter&gt;&lt;/term&gt;
          &lt;listitem&gt;
          &lt;para&gt;
  
          &lt;/para&gt;
          &lt;/listitem&gt;
      &lt;/varlistentry&gt;
      &lt;/variablelist&gt;
  &lt;/refsect1&gt;
  </code></pre>
  
  <p>But the above code doesn't work: the <em>xmlNode</em> variable is always null... What's wrong?</p>