code: function icaltime_subtract_abs(aDate) {
        var unixTime = this.toUnixTime();
        var other = aDate.toUnixTime();
        return ICAL.Duration.fromSeconds(unixTime - other);
      }
docs: Subtract the date details, taking timezones into account.
  
  @param {ICAL.Time} aDate  The date to subtract
  @return {ICAL.Duration}  The difference in duration