getDayPeriodRules(sTag) {
		const mDayPeriodRuleSet = fileContent.getContent(join(sFilePathSupple, "dayPeriods.json"))
			.supplemental.dayPeriodRuleSet;
		const oDayPeriods = mDayPeriodRuleSet[sTag];

		for (const sDayPeriodKey in oDayPeriods) {
			if (oDayPeriods[sDayPeriodKey].hasOwnProperty("_to")) {
				throw new Error("'" + sTag + "' contains deprecated property '_to'");
			} else if (oDayPeriods[sDayPeriodKey].hasOwnProperty("_after")) {
				throw new Error("'" + sTag + "' contains deprecated property '_after'");
			}
		}

		return {dayPeriodRules : mDayPeriodRuleSet[sTag.split("-")[0]]};
	}
Retrieves the "dayPeriodRuleSet" property from a given "dayPeriods.json" of a specified
locale.

@param {string} sTag The given CLDR language tag of the locale
@returns {{dayPeriodRules: Object<string, object>}}
  The JSON object, containing the "dayPeriodRules" values for the locale file of the given
  language tag
@throws {Error}
  If the given CLDR day period rule set contains the deprecated properties '_to' or '_after'

@private