# File lib/spreadsheet/worksheet.rb, line 128
    def format_column idx, format=nil, opts={}
      opts[:worksheet] = self
      res = case idx
            when Integer
              column = nil
              if format
                column = Column.new(idx, format, opts)
              end
              @columns[idx] = column
            else
              idx.collect do |col| format_column col, format, opts end
            end
      shorten @columns
      res
    end