def add_page_break(cell)
      DataTypeValidator.validate :worksheet_page_break, [String, Cell], cell
      column_index, row_index = if cell.is_a?(String)
          Axlsx.name_to_indices(cell)
        else
          cell.pos
        end
      if column_index > 0
        col_breaks.add_break(:id => column_index)
      end
      row_breaks.add_break(:id => row_index)
    end
Adds a page break (row break) to the worksheet
@param cell A Cell object or excel style string reference indicating where the break
should be added to the sheet.
@example
ws.add_page_break("A4")