description: This extension represents an US Public Health Alternative Expression package_name: hl7.fhir.us.ecr.r4b derivation: constraint name: USPublicHealthAlternativeExpressionExtension type: Extension elements: url: pattern: {type: Uri, value: 'http://hl7.org/fhir/us/ecr/StructureDefinition/us-ph-alternative-expression-extension'} index: 0 valueExpression: {type: Expression, index: 1} package_version: 2.1.1 class: extension kind: complex-type url: http://hl7.org/fhir/us/ecr/StructureDefinition/us-ph-alternative-expression-extension base: http://hl7.org/fhir/StructureDefinition/Extension version: 2.1.1