How to use the bpk-component-calendar.CustomPropTypes.DateModifiers function in bpk-component-calendar

BpkDatepicker.propTypes = {
  // Required
  changeMonthLabel: PropTypes.string.isRequired,
  closeButtonText: PropTypes.string.isRequired,
  daysOfWeek: CustomPropTypes.DaysOfWeek.isRequired,
  formatDate: PropTypes.func.isRequired,
  formatDateFull: PropTypes.func.isRequired,
  formatMonth: PropTypes.func.isRequired,
  id: PropTypes.string.isRequired,
  title: PropTypes.string.isRequired,
  getApplicationElement: PropTypes.func.isRequired,
  weekStartsOn: PropTypes.number.isRequired,
  // Optional
  calendarComponent: PropTypes.oneOfType([PropTypes.node, PropTypes.func]),
  date: PropTypes.instanceOf(Date),
  dateModifiers: CustomPropTypes.DateModifiers,
  inputProps: PropTypes.object, // eslint-disable-line react/forbid-prop-types
  markOutsideDays: PropTypes.bool,
  markToday: PropTypes.bool,
  maxDate: PropTypes.instanceOf(Date),
  minDate: PropTypes.instanceOf(Date),
  onDateSelect: PropTypes.func,
  onMonthChange: PropTypes.func,
  showWeekendSeparator: PropTypes.bool,
  initiallyFocusedDate: PropTypes.instanceOf(Date),
  renderTarget: PropTypes.func,
  isOpen: PropTypes.bool,
};

BpkDatepicker.defaultProps = {
  calendarComponent: BpkCalendar,
  date: null,