I'm learned php as functional and procedure language. Right now try to start learn objective-oriented and got an important question.

I have code:

class car {

    function set_car($model) {
        $this->model = $model;
    }

    function check_model()
    {
        if($this->model == "Mercedes") echo "Good car";
    }

}

$mycar = new car;
$mycar->set_car("Mercedes");

echo $mycar->check_model();

Why it does work without declaration of $model?

var $model; in the begin?

Because in php works "auto-declaration" for any variables? I'm stuck