simplexml xpath php, select insert update delete

<?php
$data ='<?xml version="1.0" encoding="utf-8"?>
<infos>
 <info time="1247640983" count="0" detail="will be updated" uid="1" path="/var/www/user/1/codjng.avi">MOT</info>
 <info time="1247640983" count="0" detail="will be updated" uid="2" path="/var/www/user/2/codjng.zip">HAI</info>
 <info time="1247640983" count="0" detail="will be updated" uid="3" path="/var/www/user/3/codjng-3.txt" />
</infos>';

$xml = simplexml_load_string($data);
// select
$elements = $xml->xpath("/infos/info");
foreach ($elements as $ele) {
 echo $ele[0];
}
echo "<pre>" . htmlspecialchars($xml->asXML()) . "</pre><hr/>";

// delete first element
unset($elements[0][0]);
echo "<pre>" . htmlspecialchars($xml->asXML()) . "</pre><hr/>";

// update second element
$elements[1]["path"] = "/var/www/user/2/codjng-modify.zip";
echo "<pre>" . htmlspecialchars($xml->asXML()) . "</pre>";

// insert element
$ele = $xml->addChild("info");
$ele->addAttribute("count", "1000");
$ele[0] = "bla bla codjng";
echo "<pre>" . htmlspecialchars($xml->asXML()) . "</pre>";
?>