WordPress at a glance
function is not described

WP_Widget::_register_one() public WP 2.8.0

Registers an instance of the widget class.

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

No Hooks.

Return

null. Nothing.

Usage

$WP_Widget = new WP_Widget();
$WP_Widget->_register_one( $number );
$number(int)
The unique order number of this widget instance compared to other instances of the same class.
Default: -1

Changelog

Since 2.8.0 Introduced.

Code of WP_Widget::_register_one() WP 5.7.2

<?php
public function _register_one( $number = -1 ) {
	wp_register_sidebar_widget( $this->id, $this->name, $this->_get_display_callback(), $this->widget_options, array( 'number' => $number ) );
	_register_widget_update_callback( $this->id_base, $this->_get_update_callback(), $this->control_options, array( 'number' => -1 ) );
	_register_widget_form_callback( $this->id, $this->name, $this->_get_form_callback(), $this->control_options, array( 'number' => $number ) );
}