PHP OOP Modifier and Inheritance

gistfile1.php

<?php

class Car {
  
  public $public_parent = 'public parent';
  private $private_parent = 'private parent';
  protected $protected_parent = 'protected parent';
  
  public function getCarPrivate(){
        return $this->private_parent;
  }
  public function getCarProtected(){
        return $this->protected_parent;
  }
    
}

class SportsCar extends Car{
    
    public $public_child = 'public child';
    private $private_child = 'private child';
    protected $protected_child = 'protected child';
    
    public function getProtectedParent(){
        return $this->protected_parent;
    }
    
    public function getPrivateParent(){
        return $this->private_parent;
    }
    
    public function getProtectedChild(){
        return $this->protected_child;
    }
    
    public function getPrivateChild(){
        return $this->private_child;
    }
    
}

$sports_car = new SportsCar();

//echo $sports_car->public_child; //OK
//echo $sports_car->private_child; //Exception Error: can not access
//echo $sports_car->protected_child; //Exception Error: can not access

//echo $sports_car->public_parent; //OK
//echo $sports_car->private_parent; //Error undefined
//echo $sports_car->protected_parent; //Exception Error Can not access

//echo $sports_car->getProtectedChild(); //OK
//echo $sports_car->getPrivateChild(); //OK

//echo $sports_car->getProtectedParent(); //OK
//echo $sports_car->getPrivateParent(); //Error Undefined on line return $this->private_parent;

//echo $sports_car->getCarPrivate(); //OK
//echo $sports_car->getCarProtected(); //OK


?>