DateTime::formatDateTime

static function formatDateTime($stamp, ?string $format = null): string
{
	$simple = false;

	// accept also FORMAT_DATE and FORMAT_DATETIME as ones of the legal formats
	if (
		(defined('FORMAT_DATE') && $format === FORMAT_DATE)
		|| (defined('FORMAT_DATETIME') && $format === FORMAT_DATETIME))
	{
		$format = CDatabase::dateFormatToPHP($format);
		$simple = true;
	}

	$default = static::getDateTimeFormat();
	if ($format === false)
	{
		$format = $default;
		$simple = true;
	}

	if ($simple)
	{
		// its a simple format, we can use a simpler function
		return date($format, $stamp);
	}

	return FormatDate($format, $stamp);
}