Example.php

<?php

class A {
    private function foo() {
        echo "success!\n";
    }
    public function test() {
        static::foo();
    }
}

class B extends A {
   /* foo() will be copied to B, hence its scope will still be A and
    * the call be successful */
}

class C extends A {
    private function foo() {
        /* original method is replaced; the scope of the new one is C */
        echo "failure";
    }
}

$c = new C();
$c->test(); // Fails because the private function's scope is in C and trying to access it from A will fail