title: Select parent node by children via XmlDocument
body: <p>Help please, I have the xml file,</p>
  
  <pre><code>&lt;Users&gt;
   &lt;User FullName="" Name="sa"&gt;
    &lt;userAvatarCache&gt;-1&lt;/userAvatarCache&gt;
    &lt;description&gt;&lt;/description&gt;
    &lt;email&gt;&lt;/email&gt;
    &lt;phone&gt;&lt;/phone&gt;
    &lt;UserActive&gt;true&lt;/UserActive&gt;
   &lt;/User&gt;
  
   &lt;User FullName="asfgd" Name="stest"&gt;
    &lt;userAvatarCache&gt;-1&lt;/userAvatarCache&gt;
    &lt;description&gt;aasad&lt;/description&gt;
    &lt;email&gt;test@ukr.net&lt;/email&gt;
    &lt;phone&gt;sdafdsfds0850&lt;/phone&gt;
    &lt;UserActive&gt;true&lt;/UserActive&gt;
   &lt;/User&gt;
  &lt;/Users&gt;
  </code></pre>
  
  <p>I need to select <strong>FullName</strong> by <strong>email</strong>.
  I got all structure using</p>
  
  <pre><code> XmlDocument xmlDoc = new XmlDocument();
   xmlDoc.Load(res.GetResponseStream());
   XmlNode xmlNode = xmlDoc.DocumentElement.SelectSingleNode("User");
  </code></pre>
  
  <p>Now I need only 1 result (fullname) by email.
  How I can do it correct?
  Thanks</p>