code: def _validate(self, inst: "InstanceNode", scope: ValidationScope,
                    ctype: ContentType) -> None:
          
          if (scope.value & ValidationScope.syntax.value and
                  inst.value not in self.type):
              raise YangTypeError(inst.json_pointer(), self.type.error_tag,
                                  self.type.error_message)
          if (isinstance(self.type, LinkType) and        # referential integrity
                  scope.value & ValidationScope.semantics.value and
                  self.type.require_instance):
              try:
                  tgt = inst._deref()
              except YangsonException:
                  tgt = []
              if not tgt:
                  raise SemanticError(inst.json_pointer(), "instance-required")
          super()._validate(inst, scope, ctype)
docs: Extend the superclass method.