# File lib/spreadsheet/excel/writer/workbook.rb, line 114
  def write_bof workbook, writer, type
    data = [
      @biff_version,    # BIFF version (always 0x0600 for BIFF8)
      @bof_types[type], # 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 writer, @bof, data.pack("v4V2")
  end