http://hl7.org/fhir/StructureDefinition/elementdefinition-bestpractice|5.2.0

Mark that an invariant represents 'best practice' rule - a rule that implementers may choose to enforce at error level in some or all circumstances.
typedestination
baseDefinitionhttp://hl7.org/fhir/StructureDefinition/Extension
typehttp://hl7.org/fhir/StructureDefinition/Extension
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/boolean
Extension.value[x].typehttp://hl7.org/fhir/StructureDefinition/CodeableConcept
Extension.value[x].binding.valueSethttp://hl7.org/fhir/ValueSet/use-context