code: public String describeDayOfMonth(final Map<CronFieldName, CronField> fields) {
          final String description = DescriptionStrategyFactory.daysOfMonthInstance(
                  resourceBundle,
                  fields.containsKey(CronFieldName.DAY_OF_MONTH) ? fields.get(CronFieldName.DAY_OF_MONTH).getExpression() : null
          ).describe();
          return addTimeExpressions(description, resourceBundle.getString("day"), resourceBundle.getString("days"));
      }
docs: Provide description for day of month.
  
  @param fields - fields to describe;
  @return description - String