docs: def save(self, mode=0o600):
          """
          Serialize the config data to the user home directory.
  
          :param mode: The octal Unix mode (permissions) for the config file.
          """
          if self._parent is not None:
              self._parent.save(mode=mode)
          else:
              config_dir = os.path.dirname(os.path.abspath(self.config_files[-1]))
              try:
                  os.makedirs(config_dir)
              except OSError as e:
                  if not (e.errno == errno.EEXIST and os.path.isdir(config_dir)):
                      raise
              with open(self.config_files[-1], "wb" if sys.version_info < (3, 0) else "w") as fh:
                  self._dump(fh)
              os.chmod(self.config_files[-1], mode)
              self._logger.debug("Saved config to %s", self.config_files[-1])