code: def replace_row idx, *cells
        if(row = @rows[idx]) && cells.size < row.size
          cells.concat Array.new(row.size - cells.size)
        end
        update_row idx, *cells
      end
docs: Replace the Row at _idx_ with the following arguments. Like #update_row,
   but truncates the Row if there are fewer arguments than Cells in the Row.