public function header() {
        // unfortunately YUI iframe upload does not support application/json
        if (!empty($_FILES)) {
            @header('Content-type: text/plain; charset=utf-8');
            if (!core_useragent::supports_json_contenttype()) {
                @header('X-Content-Type-Options: nosniff');
            }
        } else if (!core_useragent::supports_json_contenttype()) {
            @header('Content-type: text/plain; charset=utf-8');
            @header('X-Content-Type-Options: nosniff');
        } else {
            @header('Content-type: application/json; charset=utf-8');
        }

        // Headers to make it not cacheable and json
        @header('Cache-Control: no-store, no-cache, must-revalidate');
        @header('Cache-Control: post-check=0, pre-check=0', false);
        @header('Pragma: no-cache');
        @header('Expires: Mon, 20 Aug 1969 09:23:00 GMT');
        @header('Last-Modified: ' . gmdate('D, d M Y H:i:s') . ' GMT');
        @header('Accept-Ranges: none');
    }