Laravel 5.1: How to find "not found" L5 methods ?

For example, I am looking at the trait, "AuthenticatesUsers". It has several methods,which in turn make use of other methods. Case in point, "postLogin()" which calls, "$this->validate([])"

However, "$this->validate" can not be found anywhere. I had always believed that $this-> always referred to a method within the class, but there is not validate() method within this class.

So - is my understanding wrong or is Laravel 5.1 doing some funky stuff ?

How do I find methods with $this-> which are not in the class ? Thanks

via Chebli Mohamed