docs: def tx_extend(partial_tx_hex, new_inputs, new_outputs, blockchain='bitcoin', **blockchain_opts):
      """
      Add a set of inputs and outputs to a tx.
      Return the new tx on success
      Raise on error
      """
      if blockchain == 'bitcoin':
          return btc_tx_extend(partial_tx_hex, new_inputs, new_outputs, **blockchain_opts)
      else:
          raise ValueError('Unknown blockchain "{}"'.format(blockchain))