http://hl7.org/fhir/StructureDefinition/valueset-rules-text|5.2.0

An expression that provides an alternative definition of the content of the value set in some form that is not computable - e.g instructions that could only be followed by a human.
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/markdown