Probleme xml

$menu = <<<EOT
<nav>
    <a href="index.php?page=contact"  data-page="contact">Contact</a>
    <a href="index.php?page=liens"  data-page="liens">Liens</a>
    <a href="index.php?page=situation"  data-page="situation">Situation</a>
    <a href="index.php?page=historique"  data-page="historique">Historique</a>
    <a href="index.php?page=accueil"  data-page="accueil">Accueil</a>
</nav>
EOT;
$nav = simplexml_load_string();

foreach($nav AS $key => $link) {
    if ($link['data-page']==$page) {
        $link->addAttribute('class', 'active');
    }
}
echo str_replace('<?xml version="1.0"?>','', $nav->asXml());