code: def add(self, 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)
docs: 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.