Breakdown of contentObject

<contentObject>
  <contentKeyword> (optional - Only 1) 
  <keyXmlContent>  (use only in case only xmlObject)
  <messageSenderRole> (optional - Multiple) 
  <messageRecipientRole> (optional - Multiple)
  <confidentiality> (optional - Only 1)
  <description> (optional - Only 1)
  <mimeType> (required - Only 1)
  <size>(optional - Only 1
  <digest> (optional - Only 1)
  choice (required - only 1)
   <uri>
   <derefUri>
   <namespacedXMLcontent>