PHP OOP Tutorial 3: Implementing interfaces, utilizing structure

OOP3.php

<?php
//PHP Object Oriented Programming Tutorial 3
interface person {
    function myName();
    function myPosition();
}
class employee implements person {
    public function myName(){
        return "Happy ".  ucfirst(__CLASS__);
    }
    public function myPosition() {
        return "Lowly Jail cell cleaner";
    }
}
class executive implements person {
    public function myName(){
        return "Happy ".  ucfirst(__CLASS__);
    }
    public function myPosition() {
        return "High guy with a desk";
    }
}
class unemployed implements person {
    public function myName(){
        return "Happily ".  ucfirst(__CLASS__);
    }
    public function myPosition() {
        return "Currently outside an ally in a box";
    }
}
$array = array();
$exec = new executive();
$unem = new unemployed();
$empl = new employee();
$empl2 = new employee();
//lets put in some people into our array.
$array[] = $unem;
$array[] = $empl;
$array[] = $exec;
$array[] = $empl2;
$array[] = new DOMDocument();
foreach($array as $person){
    if($person instanceof person){
        echo $person->myName()." ".$person->myPosition()."\n";
    }
}
echo "\n";
?>