public function format_prompt($field)
    {
        $class = $this->columns[$field]['button_class'].' button_'.$field;
        $icon = isset($this->columns[$field]['icon'])
                    ? $this->columns[$field]['icon']
                    : '';
        $message = 'Enter value: ';

        $this->current_row_html[$field] =
            '<button type="button" class="'.$class.'" '.
                'onclick="value=prompt(\''.$message.'\');$(this).univ().ajaxec(\''.
                    $this->app->url(null, array(
                        $field => $this->current_id,
                        $this->name.'_'.$field => $this->current_id,
                    )).
                '&value=\'+value)"'.
            '>'.
                $icon.
                $this->columns[$field]['descr'].
            '</button>';
    }