prepare_trim_mode

# File lib/erb.rb, line 578
    def prepare_trim_mode(mode)
      case mode
      when 1
        return [false, '>']
      when 2
        return [false, '<>']
      when 0
        return [false, nil]
      when String
        perc = mode.include?('%')
        if mode.include?('-')
          return [perc, '-']
        elsif mode.include?('<>')
          return [perc, '<>']
        elsif mode.include?('>')
          return [perc, '>']
        else
          [perc, nil]
        end
      else
        return [false, nil]
      end
    end