docs: def start(self):
          """
          Iterates over the `watched_configurabes` attribute and starts a
          config file monitor for each.  The resulting observer threads are
          kept in an `observers` list attribute.
          """
          for config_class in self.watched_configurables:
              monitor = ConfigFileMonitor(config_class, self.config_dir)
              self.observers.append(
                  monitor.start(
                      self.add_configurable,
                      self.update_configurable,
                      self.remove_configurable
                  )
              )
  
          wait_on_event(self.shutdown)