# File lib/spreadsheet/excel/writer/workbook.rb, line 256
  def write_dsf workbook, writer
    data = [
      0x00, # 0 = Only the BIFF8 “Workbook” stream is present
            # 1 = Additional BIFF5/BIFF7 “Book” stream is in the file
    ]
    write_op writer, 0x0161, data.pack('v')
  end