code: public String describeDayOfWeek(final Map<CronFieldName, CronField> fields, final Map<CronFieldName, FieldDefinition> definitions) {
  
          final String description = DescriptionStrategyFactory.daysOfWeekInstance(
                  resourceBundle,
                  fields.containsKey(CronFieldName.DAY_OF_WEEK) ? fields.get(CronFieldName.DAY_OF_WEEK).getExpression() : null,
                  definitions.containsKey(CronFieldName.DAY_OF_WEEK) ? definitions.get(CronFieldName.DAY_OF_WEEK) : null
          ).describe();
          return addExpressions(description, resourceBundle.getString("day"), resourceBundle.getString("days"));
      }
docs: Provide description for day of week.
  
  @param fields - fields to describe;
  @return description - String