extraDocRef — Allows multiple documents to be associated with a single modification event
extraDocRef :  refID
     EMPTY
| refID - If an extraDocRef is used, the idRef attribute is required. | 
A single modification event may have more than one documented reference. This element can be used in place of the refID attribute in a modificationRecord to record more than one refIDs, pointing to the referenced document.
| modificationRecord | 
| NONE |