public static function connection($name, $definition = null)
	{
		if (empty($definition))
			return static::get(static::$pool, $name);

		if (static::isScalar($definition))
			list(, $dsn, $username, $password, $options) = func_get_args() + [null, '', '', '', []];
		else
			extract(static::pick($definition, ['dsn', 'username', 'password', 'options']));

		return static::$pool[$name] = new \PDO($dsn, $username, $password, $options);
	}