code: private final StringBuffer fallbackFormat(Calendar fromCalendar,
                                                Calendar toCalendar,
                                                boolean fromToOnSameDay,
                                                StringBuffer appendTo,
                                                FieldPosition pos, 
                                                String fullPattern)  {
              String originalPattern = fDateFormat.toPattern();
              fDateFormat.applyPattern(fullPattern);
              fallbackFormat(fromCalendar, toCalendar, fromToOnSameDay, appendTo, pos);
              fDateFormat.applyPattern(originalPattern);
              return appendTo;
      }
docs: /*
  Format 2 Calendars to using fall-back interval pattern
  
  This fall-back pattern is generated on a given full pattern,
  not the full pattern of the date formatter.
  
  @param fromCalendar      calendar set to the from date in date interval
  to be formatted into date interval string
  @param toCalendar        calendar set to the to date in date interval
  to be formatted into date interval string
  @param appendTo          Output parameter to receive result.
  Result is appended to existing contents.
  @param pos               On input: an alignment field, if desired.
  On output: the offsets of the alignment field.
  @param fullPattern       the full pattern need to apply to date formatter
  @return                  Reference to 'appendTo' parameter.