Using this

You should also know this before you can test the restrictor. ㅜㅜ
this is I'd like to use in my classes. Used to access a property or method declared in a class.

How to use properties using this

this->propertyname;

How to use a method using this

this-> method name();

Don't know what I'm talking about yet? You can use it like this:
Here is an example of using a property in a method:

<?php
    class Car
    {
        public $wheels = 4;

        public function checkWheelsCount()
        {
            return "This car has {$this->wheels} wheels.";
        }
    }

    $honda = new Car;
    echo $honda->checkWheelsCount();
?>

I'll check the results right below.

Result

In other words, you should not use $wheels in a class like this: $this->wheels.
The following is an example of calling another method from a method of a class.

<?php
    class Car
    {
        public $wheels = 4;

        public function checkWheelsCount()
        {
            return $this->wheels;
        }

        public function outputWheelsCount()
        {
            return "This car has {$this->checkWheelsCount()} wheels.";
        }
    }

    $honda = new Car;
    echo $honda->outputWheelsCount();
?>

I'll check the results right below.

Result

The code above functions that the method checkWheelsCount() returns the wheels property and called checkWheelsCount() in the outputWheelsCount() method.