WriteToXml method 
    
    
  
Writes to XML.
The writer.
Name of the XML element.
    
  Implementation
  void WriteToXml(EwsServiceXmlWriter writer, String xmlElementName) {
  if (this.Count > 0) {
    writer.WriteStartElement(XmlNamespace.Messages, xmlElementName);
    for (MapEntry<PropertyDefinitionBase, SortDirection> keyValuePair
        in this) {
      writer.WriteStartElement(
          XmlNamespace.Types, XmlElementNames.FieldOrder);
      writer.WriteAttributeValue(XmlAttributeNames.Order, keyValuePair.value);
      keyValuePair.key.WriteToXml(writer);
      writer.WriteEndElement(); // FieldOrder
    }
    writer.WriteEndElement();
  }
}