If the information does not exist and the cardinality of the element is >= 1…*, the Sender SHALL use the dataAbsentReason extension where it is defined. Note: populating the element with the value set absent reason or using the dataAbsent Reason SHOULD be handled by the Sending System and not require provider action.

There should be a link to the relevant extension guidance and examples of its use. The terms dataAbsentReason and dataAbsent Reason are both used; is one a mistake?

The meaning of the phrase “populating the element with the value set absent reason” is unclear. What is a “value set absetn reason”?