Symfony\Component\DomCrawler\Crawler::discoverNamespace PHP Method

    private function discoverNamespace(\DOMXPath $domxpath, $prefix)
    {
        if (isset($this->namespaces[$prefix])) {
            return $this->namespaces[$prefix];
        }
        // ask for one namespace, otherwise we'd get a collection with an item for each node
        $namespaces = $domxpath->query(sprintf('(//namespace::*[name()="%s"])[last()]', $this->defaultNamespacePrefix === $prefix ? '' : $prefix));
        if ($node = $namespaces->item(0)) {
            return $node->nodeValue;
        }
    }