def tie_breaks=(tie_breaks)
      raise "argument error - always set tie breaks to an array" unless tie_breaks.class == Array
      @tie_breaks = tie_breaks.map do |str|
        tb = ICU::TieBreak.identify(str)
        raise "invalid tie break method '#{str}'" unless tb
        tb.id
      end
    end
def tie_breaks=(tie_breaks)
      raise "argument error - always set tie breaks to an array" unless tie_breaks.class == Array
      @tie_breaks = tie_breaks.map do |str|
        tb = ICU::TieBreak.identify(str)
        raise "invalid tie break method '#{str}'" unless tb
        tb.id
      end
    end
Canonicalise the names in the tie break array.