C# XML serializer

 using System;

    
 using System.Xml;
    
 using System.Xml.Serialization;
    
 using System.IO;
    
  
    
 /* The XmlRootAttribute allows you to set an alternate name
    
    (PurchaseOrder) of the XML element, the element namespace; by
    
    default, the XmlSerializer uses the class name. The attribute
    
    also allows you to set the XML namespace for the element.  Lastly,
    
    the attribute sets the IsNullable property, which specifies whether
    
    the xsi:null attribute appears if the class instance is set to
    
    a null reference. */
    
 [XmlRootAttribute(