private function extractHiddens(&$controls, array $hiddens = null)
    {
        if (!empty($hiddens)) {
            $dom   = new \DOMDocument('1.0');
            $nodes = [];
            foreach ($hiddens as $hidden) {
                $dom->loadHTML($hidden);
                $nodes = $dom->getElementsByTagName('input');
            }
            foreach ($nodes as $node) {
                $controls[$node->getAttribute('name')] = $node->getAttribute('value');
            }
        }
    }