code: protected Formatter format(FormatterConfiguration conf, Locale locale, Object format, int start, int end, FormatArgs args) {
          try {
              if (conf == null) conf = this.conf;
              if (locale == null) locale = conf.locale();
              if (locale == null) locale = Locale.ROOT;
              String fString = toFormatString(format, locale);
              if (end < 0) end = fString.length() - end - 1;
              new Parser(conf, locale, args).parse(fString, start, end);
          } catch (IOException ex) {
              lastIOException = ex;
          }
          return this;
      }
docs: Writes a formatted string to this object's destination using the
  specified format string and arguments.
  
  @param  conf
  The formatter configuration, provides additional formats and
  the default locale. If {@code null}, the configuration specified
  at the construction of this formatter is used.
  
  @param  locale
  The {@linkplain java.util.Locale locale} to apply during
  formatting. If {@code null}, the configuration will be used to
  obtain a locale.
  
  @param  format
  A format string as described in Format string syntax. If the
  object does not implement {@link Localizable}, it is converted
  into a string.
  
  @param  start
  The index where parsing the format string begins.
  
  @param  end
  The index where parsing the format string ends
  (-1 for the entire string).
  
  @param  args
  Arguments referenced by the format specifiers in the format
  string.
  
  @throws  IllegalFormatException
  If a format string contains an illegal syntax, a format
  specifier that is incompatible with the given arguments,
  insufficient arguments given the format string, or other
  illegal conditions.
  
  @throws  FormatterClosedException
  If this formatter has been closed by invoking its {@link
  #close()} method
  
  @return  This formatter
  @see java.util.Formatter#format(java.lang.String, java.lang.Object[])