public function format_checkbox($field)
    {
        $this->current_row_html[$field] =
            '<input type="checkbox" '.
                'id="cb_'.$this->current_id.'" '.
                'name="cb_'.$this->current_id.'" '.
                'value="'.$this->current_id.'" '.
                ($this->current_row['selected'] == 'Y'
                    ? 'checked '
                    : ''
                ).
            '/>';
        $this->setTDParam($field, 'width', '10');
        $this->setTDParam($field, 'align', 'center');
    }