WordPress at a glance
function is not described

_register_widget_update_callback() WP 2.8.0

Registers the update callback for a widget.

  • Global. Array. $wp_registered_widget_updates

No Hooks.

Return

Nothing (null).

Usage

_register_widget_update_callback( $id_base, $update_callback, $options );
$id_base(string) (required)
The base ID of a widget created by extending WP_Widget.
$update_callback(callable) (required)
Update callback method for the widget.
$options(array)
Widget control options. See wp_register_widget_control().
Default: empty array

Code of register widget update callback: wp-includes/widgets.php WP 5.2.2

<?php
function _register_widget_update_callback( $id_base, $update_callback, $options = array() ) {
	global $wp_registered_widget_updates;

	if ( isset( $wp_registered_widget_updates[ $id_base ] ) ) {
		if ( empty( $update_callback ) ) {
			unset( $wp_registered_widget_updates[ $id_base ] );
		}
		return;
	}

	$widget = array(
		'callback' => $update_callback,
		'params'   => array_slice( func_get_args(), 3 ),
	);

	$widget                                   = array_merge( $widget, $options );
	$wp_registered_widget_updates[ $id_base ] = $widget;
}