code: public String combineDateAndTime(String relativeDateString, String timeString) {
          return SimpleFormatterImpl.formatCompiledPattern(
                  combinedDateAndTime, timeString, relativeDateString);
      }
docs: Combines a relative date string and a time string in this object's
  locale. This is done with the same date-time separator used for the
  default calendar in this locale.
  @param relativeDateString the relative date e.g 'yesterday'
  @param timeString the time e.g '3:45'
  @return the date and time concatenated according to the default
  calendar in this locale e.g 'yesterday, 3:45'