PHP Decorator pattern

decorator.php

<?php

abstract class AbstractWindow
{
    protected $_title;
    
    public function __construct($title = null)
    {
        $this->_title = $title;
    }
    
    abstract public function draw();
}

class LinuxWindow extends AbstractWindow
{
    public function draw()
    {
        return 'Linux Window "' . $this->_title . '"';
    }
}

class OsxWindow extends AbstractWindow
{
    public function draw()
    {
        return 'OsX Window "' . $this->_title . '"';
    }
}

abstract class AbstractWindowDecorator extends AbstractWindow
{
    protected $_window;
    
    public function __construct(AbstractWindow $window)
    {
        $this->_window = $window;
    }
}

class BorderedWindow extends AbstractWindowDecorator
{
    public function draw()
    {
        return 'Bordered ' . $this->_window->draw();
    }
}

class TransparentWindow extends AbstractWindowDecorator
{    
    public function draw()
    {
        return 'Transparent ' . $this->_window->draw();
    }
}

$window = new TransparentWindow(new BorderedWindow(new LinuxWindow("About...")));

echo $window->draw();