PlaneString::getMultiByteConstant

protected function getMultiByteConstant(?string $letterCase): ?int
{
	$map = [
		static::LETTER_CASE_LOWER => MB_CASE_LOWER,
		static::LETTER_CASE_UPPER => MB_CASE_UPPER,
		static::LETTER_CASE_TITLE => MB_CASE_TITLE,
	];

	return $map[$letterCase] ?? null;
}