code: public WorkingWeek intersection(final WorkingWeek ww) {
          final byte combined = (byte) (this.workingDays & ww.workingDays);
          return new WorkingWeek(combined);
      }
docs: Create a new calendar with the intersection of WORKING days.
  e.g. if normal and arabic calendars are intersected, the week is 3 days: Fri-Sun.
  @param ww
  @return a new Working week
  @since 1.4.0