http://hl7.org/fhir/StructureDefinition/cqf-modelInfo-isRetrievable|5.2.0

Specifies whether the class constructed for the profile should be marked as retrievable in the model info (meaning whether or not it can appear as the target of a retrieve expression). If this value is not specified, retrievable is true for resources and false for data types.
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.url.typehttp://hl7.org/fhir/StructureDefinition/uri
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/boolean