This case-sensitive code system http://hl7.org/fhir/codesystem-altcode-kind defines the following codes:

Code	Display	Definition
alternate	Alternate Code	The code is an alternative code that can be used in any of the circumstances that the primary code can be used.
deprecated	Deprecated	The code should no longer be used, but was used in the past.
case-insensitive	Case Insensitive	The code is an alternative to be used when a case insensitive code is required (when the primary codes are case sensitive).
case-sensitive	Case Sensitive	The code is an alternative to be used when a case sensitive code is required (when the primary codes are case insensitive).
expression	Expression	The code is an alternative for the primary code that is built using the expression grammar defined by the code system.