Inheritance example for habrahabr

inh_ex.php

<?php

class A {
    public function setSize($x, $y) {
        print('A');
    }
}

class B extends A {
    public function setSize($x) {
        print('B');
    }
}

$a = new A();
$a->setSize(1, 2);

$b = new B();
$b->setSize(1);
$b->setSize(1, 2);

Output:
ABB

Because php allows you to pass to functions any number of arguments