import tensorflow as tf

      the decoded items, a list of tensor.
    """
    context, sequence = tf.parse_single_sequence_example(
        serialized_example, self._context_keys_to_features,
        self._sequence_keys_to_features)
    tokens_raw = sequence[self.tokens_feature_name]
    
    tokens = tf.string_split(tokens_raw, delimiter=self.delimiter).values

    # Optionally prepend a special token
    if self.prepend_token is not None:
      tokens = tf.concat([[self.prepend_token], tokens], 0)

    # Optionally append a special token
