SimpleXML: Añadir elementos y atributos

<?xml version="1.0" encoding="UTF-8"?>
<feed>
    ...
    <movie>
        <characters>
            <character>
                <name>Megan</name>
                <actor>Anna Smith</actor>
            </character>
        </characters>
    </movie>
    ...
</feed>

<?xml version="1.0" encoding="UTF-8"?>
<feed>
    ...
    <movie>
        <characters>
            <character>
                <name>Megan</name>
                <actor>Anna Smith</actor>
            </character>
            <character>
                <name>Mr. Parser</name>
                <actor>John Doe</actor>
            </character>
        </characters>
        <rating type="mpaa">PG</rating>
    </movie>
    ...
</feed>

<?php
$feed = "http://www.domain.com/feed/info.xml";
// volcar el feed en un objeto SimpleXML
$xml = simplexml_load_file($feed);
 
// añadir character
$character = $xml->movie[0]->characters->addChild('character');
$character->addChild('name', 'Mr. Parser');
$character->addChild('actor', 'John Doe');
 
// añadir rating
$rating = $xml->movie[0]->addChild('rating', 'PG');
$rating->addAttribute('type', 'mpaa');
?>