title: how to represent \r or \n or \t in XML and read them back correctly using XmlDocument
body: <p>For example:</p>
  
  <pre><code>&lt;codes&gt;\n\r\t&lt;/codes&gt;
  </code></pre>
  
  <p>When I read the node "codes" in a string, it should contain the 3 characters <code>'\n'</code>, <code>'\r'</code>, <code>'\t'</code> as if it was <code>s="\n\r\t";</code></p>