protected function add_autovalues(&$attrs)
    {
        if (empty($this->prop['autovalues'])) {
            return;
        }

        $attrvals = array();
        foreach ($attrs as $k => $v) {
            $attrvals['{'.$k.'}'] = is_array($v) ? $v[0] : $v;
        }

        foreach ((array)$this->prop['autovalues'] as $lf => $templ) {
            if (empty($attrs[$lf])) {
                if (strpos($templ, '(') !== false) {
                    // replace {attr} placeholders with (escaped!) attribute values to be safely eval'd
                    $code = preg_replace('/\{\w+\}/', '', strtr($templ, array_map('addslashes', $attrvals)));
                    $res  = false;

                    try {
                        $res = eval("return ($code);");
                    }
                    catch (ParseError $e) {
                        // ignore
                    }

                    if ($res === false) {
                        rcube::raise_error(array(
                            'code' => 505, 'file' => __FILE__, 'line' => __LINE__,
                            'message' => "Expression parse error on: ($code)"), true, false);
                        continue;
                    }

                    $attrs[$lf] = $res;
                }
                else {
                    // replace {attr} placeholders with concrete attribute values
                    $attrs[$lf] = preg_replace('/\{\w+\}/', '', strtr($templ, $attrvals));
                }
            }
        }
    }