public function lowerCaseRoman($s, $matchMode = 'strict') : string
	{
		$result = RomanNumerals::romanNumeralMatchCallback(
			$s,
			$matchMode,
			function (array $matches) {
				if (empty($matches[1])) {
					return $matches[1];
				}
				return strtolower($matches[1]);
			}
		);
		return $result;
	}