Vytvoření RSS v OOP

<?php
class RSS {
  private $title, $link, $description, $language;
  private $image_title, $image_url, $image_link, $image_width, $image_height;
  private $items = array();

  public function __construct($title, $link, $description, $language){
    $this->title = $title;
    $this->link = $link;
    $this->description = $description;
    $this->language = $language;
  }

  public function setImage($title, $url, $link, $width, $height){
    $this->image_title = $title;
    $this->image_url = $url;
    $this->image_link = $link;
    $this->image_width = $width;
    $this->image_height = $height;
  }

  public function setItems($items){
    $return = "";
    foreach($items as $item){
      $return .= $item;
    }
    $this->items = $return;
  }

  public function __toString(){
    return '<?xml version="1.0" encoding="UTF-8"?>
    <rss version="0.91">
      <channel>
        <title>'.$this->title.'</title>
        <link>http://'.$this->link.'</link>
        <description>'.$this->description.'</description>
        <language>'.$this->language.'</language>
        <image>
          <title>'.$this->image_title.'</title>
          <url>'.$this->image_url.'</url>
          <link>'.$this->image_link.'</link>
          <width>'.$this->image_width.'</width>
          <height>'.$this->image_height.'</height>
        </image>

        '.$this->items.'

      </channel>
    </rss>';
  }
}

class RSS_item {
  private $title, $link, $description, $pubDate;

  public function __construct($title, $link, $description, $pubDate){
    $this->title = $title;
    $this->link = $link;
    $this->description = $description;
    $this->pubDate = $pubDate;
  }

  public function __toString(){
    return "<item>
    <title>".$this->title."</title>
    <link>".$this->link."</link>
    <description>".$this->description."</description>
    <pubDate>".$this->pubDate."</pubDate>
    </item>";
  }
}
?>

<?php
$rss = new RSS("title", "link", "description", "language");
$rss->setItems(array(new RSS_item("title 1","link 1","description 1","Sat, 18 May 2002 15:21:36 GMT"),
                     new RSS_item("title 2","link 2","description 2","Sun, 19 May 2002 15:21:36 GMT"),
                     new RSS_item("title 3","link 3","description 3","Mon, 20 May 2002 15:21:36 GMT")
                     ));
echo $rss;
?>

  public function addItem($item){
    if(is_object($item) && get_class($item) == "RSS_item")
      $this->items .= $item;
  }