code: private boolean isWorkingDate(Date date, Day day)
     {
        ProjectCalendarDateRanges ranges = getRanges(date, null, day);
        return ranges.getRangeCount() != 0;
     }
docs: This private method allows the caller to determine if a given date is a
  working day. This method takes account of calendar exceptions. It assumes
  that the caller has already calculated the day of the week on which
  the given day falls.
  
  @param date Date to be tested
  @param day Day of the week for the date under test
  @return boolean flag