Source

File: wp-includes/IXR/class-IXR-error.php

function getXml()
    {
        $xml = <<<EOD
<methodResponse>
  <fault>
    <value>
      <struct>
        <member>
          <name>faultCode</name>
          <value><int>{$this->code}</int></value>
        </member>
        <member>
          <name>faultString</name>
          <value><string>{$this->message}</string></value>
        </member>
      </struct>
    </value>
  </fault>
</methodResponse>

EOD;
        return $xml;
    }