docs: def on_modified(self, event):
          """
          Modified config file handler.
  
          If a config file is modified, the yaml contents are parsed and the
          new results are validated by the target class.  Once validated, the
          new config is passed to the on_update callback.
          """
          if os.path.isdir(event.src_path):
              return
  
          logger.debug("file modified: %s", event.src_path)
  
          name = self.file_name(event)
  
          try:
              config = yaml.load(open(event.src_path))
              self.target_class.from_config(name, config)
          except Exception:
              logger.exception(
                  "Error when loading updated config file %s", event.src_path,
              )
              return
  
          self.on_update(self.target_class, name, config)