# File lib/spreadsheet/excel/writer/worksheet.rb, line 131
  def write_bof
    data = [
      @biff_version, # BIFF version (always 0x0600 for BIFF8)
      0x0010,        # Type of the following data:
                     # 0x0005 = Workbook globals
                     # 0x0006 = Visual Basic module
                     # 0x0010 = Worksheet
                     # 0x0020 = Chart
                     # 0x0040 = Macro sheet
                     # 0x0100 = Workspace file
      @build_id,     # Build identifier
      @build_year,   # Build year
      0x000,         # File history flags
      0x006,         # Lowest Excel version that can read
                     # all records in this file
    ]
    write_op @bof, data.pack("v4V2")
  end