public function removeCustomNamespaces(SourceEvent $event)
{
$template = $event->getTemplate();
foreach ($this->customNamespaces as $prefix => $ns) {
$template = preg_replace('#<(.*) xmlns:' . $prefix . '="' . $ns . '"(.*)>#mi', "<\\1\\2>", $template);
}
$event->setTemplate($template);
}