scope resolution operator / visibility

[Anon]

When using the scope resolution operator. Does anyone know how a non-inherited class' method can have visibility from within another class? I've seen this working, but I'm not sure how it was done.

Like:

class Cone
{

function showGreeting()
{
	echo 'hi, from Cone';	
}

}

class Cone2 // extends Cone // this works, but only if Cone is extended
{

function display()
{
	Cone::showGreeting(); 
}

}

$myObj2 = new Cone2();
$myObj2->display();