public static function extractStrings(DOMElement $parent, string $namespaceURI, string $localName) : array
    {
        $ret = [];
        foreach ($parent->childNodes as $node) {
            if ($node->namespaceURI !== $namespaceURI || $node->localName !== $localName) {
                continue;
            }
            $ret[] = trim($node->textContent);
        }

        return $ret;
    }