Append a cell into the stack.

        Parameters
        ----------
        cell : BaseRNNCell
            The cell to be appended. During unroll, previous cell's output (or raw inputs if
            no previous cell) is used as the input to this cell.

def add(self, cell):
        """Append a cell into the stack.

        Parameters
        ----------
        cell : BaseRNNCell
            The cell to be appended. During unroll, previous cell's output (or raw inputs if
            no previous cell) is used as the input to this cell.
        """
        self._cells.append(cell)
        if self._override_cell_params:
            assert cell._own_params, \
                "Either specify params for SequentialRNNCell " \
                "or child cells, not both."
            cell.params._params.update(self.params._params)
        self.params._params.update(cell.params._params)