Update mode. Should always be umNull in a CDA document
umA: Add : The item was (or is to be) added, having not been present immediately before. (If it is already present, this may be treated as an error condition.)
umD: Remove : The item was (or is to be) removed (sometimes referred to as deleted). If the item is part of a collection, delete any matching items.
umR: Replace : The item existed previously and has been (or is to be) revised. (If an item does not already exist, this may be treated as an error condition.)
umAR: Add or Replace : The item was (or is to be) either added or replaced. No assertion is made as to whether the item previously existed
umN: No Change : There was (or is to be) no change to the item. This is primarily used when this element has not changed, but other attributes in the instance have changed.
umU: Unknown : It is not specified whether or what kind of change has occurred to the item, or whether the item is present as a reference or identifying property.
umK: Key : This item is part of the identifying information for the object that contains it