See base class for details.

def save_metadata(self, data_dir, feature_name=None):
    """See base class for details."""
    # 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)