protected static function _checksum(array $token, $isString) {
		$token['checksum'] = static::$_bracketsChecksum;
		if ($isString) {
			return $token;
		}
		$char = $token['content'];
		if ($char === ')' || $char === ']' || $char === '}') {
			$token['checksum'] = --static::$_bracketsChecksum;
		} elseif ($char === '(' || $char === '[' || $char === '{') {
			static::$_bracketsChecksum++;
		}
		return $token;
	}