I am confuse of this login() method

Hi,Can you help me please to enligthen my mind.In LoginForm.php.

in this part of code

I am confuse where this Yii::$app->user->login(); come from, having two parameters.

I am looking in the yii2 references Model

but I could not find that login method having two parameters.

can you please engligthen my mind.

Thank you in advance.

Login method (Yii::$app->user->login()) you are finding here:

http://www.yiiframework.com/doc-2.0/yii-web-user.html#login()-detail

Thank you :)