This code system http://hl7.org/fhir/sort-direction defines the following codes:

Code Display Definition
ascending Ascending Sort by the value ascending, so that lower values appear first.
descending Descending Sort by the value descending, so that lower values appear last.
<status value="draft"/> <experimental value="false"/> <date value="2023-03-26T15:21:02+11:00"/> <publisher value="HL7 (FHIR Project)"/> <contact> <telecom> <system value="url"/> <value value="http://hl7.org/fhir"/> </telecom> <telecom> <system value="email"/> <value value="fhir@lists.hl7.org"/> </telecom> </contact> <description value="The possible sort directions, ascending or descending."/> <jurisdiction> <coding> <system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/> <code value="001"/> <display value="World"/> </coding> </jurisdiction> <caseSensitive value="true"/> <valueSet value="http://hl7.org/fhir/ValueSet/sort-direction"/> <content value="complete"/> <concept> <code value="ascending"/> <display value="Ascending"/> <definition value="Sort by the value ascending, so that lower values appear first."/> </concept> <concept> <code value="descending"/> <display value="Descending"/> <definition value="Sort by the value descending, so that lower values appear last."/> </concept> </CodeSystem>