description: allow for a check digit and a check digit scheme to be conveyed as part of Identifier. The rules of the ID Type determine if the check digit is part of the ID value or sent separately. package_name: hl7.fhir.r5.examples derivation: constraint name: checkDigit type: Extension elements: extension: {index: 0} url: pattern: {type: Uri, value: 'http://hl7.org/fhir/StructureDefinition/identifier-checkDigit'} index: 1 value: choices: [valueString] index: 3 valueString: {type: string, choiceOf: value, index: 4} package_version: 5.0.0-ballot extensions: {} class: extension kind: complex-type url: http://hl7.org/fhir/StructureDefinition/identifier-checkDigit base: http://hl7.org/fhir/StructureDefinition/Extension version: 5.0.0-ballot required: [valueString, value]