What is the difference between calling parent::__construct and self::__construct in PHP when dealing with inheritance?

When dealing with inheritance in PHP, calling `parent::__construct()` refers to invoking the constructor of the parent class, while calling `self::__construct()` refers to invoking the constructor of the current class itself. It is important to use `parent::__construct()` when you want to initialize the parent class properties before initializing the current class properties. Using `self::__construct()` may lead to unexpected behavior or errors in the inheritance chain.

class ParentClass {
    public function __construct() {
        echo "Parent constructor called";
    }
}

class ChildClass extends ParentClass {
    public function __construct() {
        parent::__construct(); // Call parent constructor
        echo "Child constructor called";
    }
}

$child = new ChildClass();