RSS generation class instance implemented by php, phprss generation instance_PHP tutorial

class RSS
{
 var $title;
 var $link;
 var $description;
 var $language = "en-us";
 var $pubDate;
 var $items;
 var $tags;
 function RSS()
 {
  $this->items = array();
  $this->tags = array();
 }
 function addItem($item)
 {
  $this->items[] = $item;
 }
 function setPubDate($when)
 {
  if(strtotime($when) == false)
   $this->pubDate = date("D, d M Y H:i:s ", $when) . "GMT";
  else
   $this->pubDate = date("D, d M Y H:i:s ", strtotime($when)) . "GMT";
 }
 function getPubDate()
 {
  if(empty($this->pubDate))
   return date("D, d M Y H:i:s ") . "GMT";
  else
   return $this->pubDate;
 }
 function addTag($tag, $value)
 {
  $this->tags[$tag] = $value;
 }
 function out()
 {
  $out = $this->header();
  $out .= "<channel>\n";
  $out .= "<title>" . $this->title . "</title>\n";
  $out .= "<link>" . $this->link . "</link>\n";
  $out .= "<description>" . $this->description . "</description>\n";
  $out .= "<language>" . $this->language . "</language>\n";
  $out .= "<pubDate>" . $this->getPubDate() . "</pubDate>\n";
  foreach($this->tags as $key => $val) $out .= "<$key>$val</$key>\n";
  foreach($this->items as $item) $out .= $item->out();
  $out .= "</channel>\n";
  $out .= $this->footer();
  $out = str_replace("&", "&", $out);
  return $out;
 }
 function serve($contentType = "application/xml")
 {
  $xml = $this->out();
  header("Content-type: $contentType");
  echo $xml;
 }
 function header()
 {
  $out = '<&#63;xml version="1.0" encoding="utf-8"&#63;>' . "\n";
  $out .= '<rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/">' . "\n";
  return $out;
 }
 function footer()
 {
  return '</rss>';
 }
}
class RSSItem
{
 var $title;
 var $link;
 var $description;
 var $pubDate;
 var $guid;
 var $tags;
 var $attachment;
 var $length;
 var $mimetype;
 function RSSItem()
 { 
  $this->tags = array();
 }
 function setPubDate($when)
 {
  if(strtotime($when) == false)
   $this->pubDate = date("D, d M Y H:i:s ", $when) . "GMT";
  else
   $this->pubDate = date("D, d M Y H:i:s ", strtotime($when)) . "GMT";
 }
 function getPubDate()
 {
  if(empty($this->pubDate))
   return date("D, d M Y H:i:s ") . "GMT";
  else
   return $this->pubDate;
 }
 function addTag($tag, $value)
 {
  $this->tags[$tag] = $value;
 }
 function out()
 {
  $out .= "<item>\n";
  $out .= "<title>" . $this->title . "</title>\n";
  $out .= "<link>" . $this->link . "</link>\n";
  $out .= "<description>" . $this->description . "</description>\n";
  $out .= "<pubDate>" . $this->getPubDate() . "</pubDate>\n";
  if($this->attachment != "")
   $out .= "<enclosure url='{$this->attachment}' length='{$this->length}' type='{$this->mimetype}' />";
  if(empty($this->guid)) $this->guid = $this->link;
  $out .= "<guid>" . $this->guid . "</guid>\n";

  foreach($this->tags as $key => $val) $out .= "<$key>$val</$key\n>";
  $out .= "</item>\n";
  return $out;
 }
 function enclosure($url, $mimetype, $length)
 {
  $this->attachment = $url;
  $this->mimetype  = $mimetype;
  $this->length   = $length;
 }
}

$feed = new RSS();
$feed->title    = "RSS Feed Title";
$feed->link    = "http://website.com";
$feed->description = "Recent articles on your website.";
$db->query($query);
$result = $db->result;
while($row = mysql_fetch_array($result, MYSQL_ASSOC))
{
  $item = new RSSItem();
  $item->title = $title;
  $item->link = $link;
  $item->setPubDate($create_date); 
  $item->description = "<![CDATA[ $html ]]>";
  $feed->addItem($item);
}
echo $feed->serve();