Abstract Properties in PHP

<?php
abstract class Art {
    public static function getDescription(){
        if(!isset(static::$Description)) {throw new UnexpectedValueException(get_called_class() . ' must define a static Description property');}
        return static::$Description;
    }
}

interface Drawing{
    public function Draw();
    public function Delete();
}

abstract class Shape extends Art implements Drawing {
    abstract public function Draw();
    public function Delete(){echo "Deleted the " . static::getDescription() . "\n";}
}

class Square extends Shape {
    protected static $Description = "Square";
    public function Draw(){echo "Drawing something with four sides....\n";}
}
class Circle extends Shape {
    protected static $Description = "Circle";
    public function Draw(){echo "Drawing something round....\n";}
}
?>

<pre>
<?php
echo "Avialable Items to draw:\n";
echo Square::getDescription() . ", " . Circle::getDescription() . "\n\n";

$shape1 = new Square();
$shape2 = new Circle();

$shape1->Draw();
$shape2->Draw();
$shape1->Delete();
$shape2->Delete();
?>
</pre>