description: Record of the date and/or time of the first exposure to the Substance for this Reaction Event. package_name: hl7.fhir.uv.extensions derivation: constraint name: AIExposureDate type: Extension elements: extension: {index: 0} url: pattern: {type: Uri, value: 'http://hl7.org/fhir/StructureDefinition/openEHR-exposureDate'} index: 1 value: choices: [valueDateTime] index: 3 valueDateTime: {type: dateTime, choiceOf: value, index: 4} package_version: 5.1.0-snapshot1 extensions: {} class: extension kind: complex-type url: http://hl7.org/fhir/StructureDefinition/openEHR-exposureDate base: http://hl7.org/fhir/StructureDefinition/Extension version: 5.1.0-snapshot1 required: [valueDateTime, value]