http://hl7.org/fhir/StructureDefinition/operationdefinition-allowed-type|5.2.0

When the base type is an abstract type (e.g. Resource or Element) then this extension defines which concrete types are allowed to be used for a parameter. In the absence of this extension, any type is allowed. Replaced by OperationDefinition.parameter.allowedType in R5+
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/uri