# File lib/spreadsheet/workbook.rb, line 31
   def add_format(*args)
      if args[0].kind_of?(Hash)
         f = Format.new(args[0], @xf_index)
      elsif args[0].nil?
         f = Format.new
      else
         raise TypeError unless args[0].kind_of?(Format)
         f = args[0]
         f.xf_index = @xf_index
      end
      @xf_index += 1
      @formats.push(f)
      return f
   end