phpeveryday.com

<?php
$lib  = simplexml_load_file("test.xml");
$lib->book->asXML("test2.txt");

?>

Result become like this:

<book>
  <id>1</id>
  <title>PHP AJAX</title>
  <author>Andreas</author>
  <description>This is good book for learning AJAX</description>
  <on_sale>1</on_sale>
</book>

From above, we take one subtree and enter to new file named "test2.xml". From code above, you can practice with other such as:

<?php
$lib  = simplexml_load_file("test.xml");

$title = $lib->book->title;
$title->asXML("test2.txt");

?>