public function get_outermost_quote_authors($xml)
{
$authors = array();
if (strpos($xml, '<QUOTE ') === false) {
return $authors;
}
$dom = new \DOMDocument();
$dom->loadXML($xml);
$xpath = new \DOMXPath($dom);
foreach ($xpath->query('//QUOTE[not(ancestor::QUOTE)]/@author') as $author) {
$authors[] = $author->textContent;
}
return $authors;
}