code: def save_metadata(self, data_dir, feature_name=None):
      
      # Recursively save all child features
      for feature_key, feature in six.iteritems(self._feature_dict):
        if feature_name:
          feature_key = '-'.join((feature_name, feature_key))
        feature.save_metadata(data_dir, feature_name=feature_key)
docs: See base class for details.