WP_Widget_Recent_Comments::update( array $new_instance, array $old_instance )

Source

File: wp-includes/widgets/class-wp-widget-recent-comments.php

public function update( $new_instance, $old_instance ) {
		$instance           = $old_instance;
		$instance['title']  = sanitize_text_field( $new_instance['title'] );
		$instance['number'] = absint( $new_instance['number'] );
		return $instance;
	}