title: SecurityElement.IsValidText returns true on "&" ... why?
body: <p>I have a TextBox that is eventually saved in a xml node. I am using the <strong>SecurityElement.Escape(string2Escape)</strong> to escape the invalid characters before saving the xml.</p>
  
  <p>Problem: I tried using the IsValidText to test if i need to run the escape method, but it returns ''' and '&amp;' as valid but then when you save the xml the system barfs because they are, in fact, not valid. It seems to only return false on '&lt;' or '>'.</p>
  
  <p>Simple solution, remove the check, but my question is why would this be the case?</p>
  
  <p>The following is my failing code:</p>
  
  <pre><code>private string EscapeXML(string nodeText)
  {
      if (!SecurityElement.IsValidText(nodeText))
      {
          return SecurityElement.Escape(nodeText);
      }
      return nodeText;
  }
  </code></pre>