docs: def _handle_class_instance(self, klass):
          """
          handles class instances. If a class is blacklisted, returns.
          If uniuqe_instances is True and the class is unique, instantiates
          the class and adds the new object to plugins.
  
          If not unique_instances, creates and adds new instance to plugin
          state
          """
          if (klass in self.blacklisted_plugins or not
                  self.instantiate_classes or
                  klass == IPlugin):
              return
          elif self.unique_instances and self._unique_class(klass):
              self.plugins.append(klass())
          elif not self.unique_instances:
              self.plugins.append(klass())