This code system http://hl7.org/fhir/v2/0397 defines the following codes:

CodeDisplay
AAscending
ANAscending, case insensitive
DDescending
DNDescending, case insensitive
NNone

Additional Language Displays

CodeNederlands (Dutch, nl)
AOplopend
ANOplopend, niet-hoofdlettergevoelig
DAflopend
DNAflopend, niet-hoofdlettergevoelig
NGeen