正则表达实现rss解析

<?php$str='<title>Our Demo RSS</title>      <link>http://www.tracypeterson.com/RSS/RSS.php</link>      <description>A Test RSS</description>      <language>en-us</language>      <pubDate>$now</pubDate>      <lastBuildDate>$now</lastBuildDate>      <docs>http://someurl.com</docs>      <managingEditor>[e-mail]</managingEditor>      <webMaster>[e-mail]</webMaster>';preg_match_all('/tle>(.*)</', $str, $v[0]);preg_match_all('/ocs>(.*)</', $str, $v[1]);preg_match_all('/ion>(.*)</', $str, $v[2]);for($j=0;$j<3;$j++){var_dump($v[$j][1]);echo "<br>";}?>