WordPress at a glance
function is not described

WP_Widget_RSS::update() public WP 2.8.0

Handles updating settings for the current RSS widget instance.

{} It's a method of the class: WP_Widget_RSS{}

No Hooks.

Return

Array. Updated settings to save.

Usage

$WP_Widget_RSS = new WP_Widget_RSS();
$WP_Widget_RSS->update( $new_instance, $old_instance );
$new_instance(array) (required)
New settings for this instance as input by the user via WP_Widget::form().
$old_instance(array) (required)
Old settings for this instance.

Changelog

Since 2.8.0 Introduced.

Code of WP_Widget_RSS::update() WP 5.7.2

<?php
public function update( $new_instance, $old_instance ) {
	$testurl = ( isset( $new_instance['url'] ) && ( ! isset( $old_instance['url'] ) || ( $new_instance['url'] !== $old_instance['url'] ) ) );
	return wp_widget_rss_process( $new_instance, $testurl );
}