This code system http://terminology.hl7.org/CodeSystem/codesystem-altcode-kind defines the following codes:

CodeDisplayDefinition
alternate Alternate CodeThe code is an alternative code that can be used in any of the circumstances that the primary code can be used.
deprecated DeprecatedThe code should no longer be used, but was used in the past.
case-insensitive Case InsensitiveThe code is an alternative to be used when a case insensitive code is required (when the primary codes are case sensitive).
case-sensitive Case SensitiveThe code is an alternative to be used when a case sensitive code is required (when the primary codes are case insensitive).
expression ExpressionThe code is an alternative for the primary code that is built using the expression grammar defined by the code system.
 <status value="draft"/> <experimental value="false"/> <date value="2020-04-09T21:10:28+00:00"/> <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="Indicates the type of use for which the code is defined."/> <caseSensitive value="true"/> <valueSet value="http://terminology.hl7.org/ValueSet/codesystem-altcode-kind"/> <content value="complete"/> <concept> <code value="alternate"/> <display value="Alternate Code"/> <definition value="The code is an alternative code that can be used in any of the circumstances that the primary code can be used."/> </concept> <concept> <code value="deprecated"/> <display value="Deprecated"/> <definition value="The code should no longer be used, but was used in the past."/> </concept> <concept> <code value="case-insensitive"/> <display value="Case Insensitive"/> <definition value="The code is an alternative to be used when a case insensitive code is required (when the primary codes are case sensitive)."/> </concept> <concept> <code value="case-sensitive"/> <display value="Case Sensitive"/> <definition value="The code is an alternative to be used when a case sensitive code is required (when the primary codes are case insensitive)."/> </concept> <concept> <code value="expression"/> <display value="Expression"/> <definition value="The code is an alternative for the primary code that is built using the expression grammar defined by the code system."/> </concept> </CodeSystem>