next_widget_id_number

	global $wp_registered_widgets;
	$number = 1;

	foreach ( $wp_registered_widgets as $widget_id => $widget ) {
		if ( preg_match( '/' . $id_base . '-([0-9]+)$/', $widget_id, $matches ) ) {
			$number = max( $number, $matches[1] );
		}
	}
	$number++;

	return $number;
}