WordPress at a glance
filter is not described

widget_update_callback filter-hook . WP 2.8.0

Filters a widget's settings before saving.

Returning false will effectively short-circuit the widget's ability to update settings.

Usage

add_filter( 'widget_update_callback', 'filter_function_name_6107', 10, 4 );
function filter_function_name_6107( $instance, $new_instance, $old_instance, $this ){
	// filter...

	return $instance;
}
$instance(array)
The current widget instance's settings.
$new_instance(array)
Array of new widget settings.
$old_instance(array)
Array of old widget settings.
$this(WP_Widget)
The current widget instance.

Where the hook is called

WP_Widget::update_callback()
wp-includes/class-wp-widget.php 451
$instance = apply_filters( 'widget_update_callback', $instance, $new_instance, $old_instance, $this );

Where the hook is used (in WP core)

Does not used.