# File htree/encoder.rb, line 32
    def output_string(internal_str, external_str=@ic.iconv(internal_str))
      @buf << external_str
      @subcharset_ic.reject! {|subcharset, ic|
        begin
          ic.iconv(internal_str) != external_str
        rescue Iconv::Failure
          true
        end
      }
      nil
    end