public function add_highlight_content($response) {
        if (!isset($response->highlighting)) {
            // There is no highlighting to add.
            return;
        }

        $highlightedobject = $response->highlighting;
        foreach ($response->response->docs as $doc) {
            $x = $doc->id;
            $highlighteddoc = $highlightedobject->$x;
            $this->merge_highlight_field_values($doc, $highlighteddoc);
        }
    }