How can PHP be used to load and play external content, such as XML files, in Flash?

To load and play external content, such as XML files, in Flash using PHP, you can create a PHP script that reads the XML file and outputs it as a response. Then, in your Flash application, you can use the `URLLoader` class to load the PHP script and parse the XML data.

<?php
$xmlFile = 'external_content.xml';
header('Content-Type: text/xml');
readfile($xmlFile);
?>