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RecordIdentifier must be present. It identifies the record to be replaced.
RecordVersions may be present. If present, they further identify the record to be replaced.
Record must be present.
It is recommended that RecordIdentifer be present. It identifies the new record.
RecordVersions may be present. If present, it identifies the new record.
Record may be present. It is recommended that it be present if the server has transformed the received record in any way.