This function had been marked as deprecated since 2.8.0. Use wp_register_widget_control()

Registers widget control callback for customizing options.

Allows $name to be an array that accepts either three elements to grab the first element and the third for the name or just uses the first element of the array for the name.

Passes to {@link wp_register_widget_control()} after the argument list has been compiled.

Signature

register_widget_control( $name, $control_callback, $width = '', $height = '' )
name
 (int|string) Sidebar ID.
control_callback
 (callback) Widget control callback to display and process form.
width
 (int) Widget width.
Default: ''
height
 (int) Widget height.
Default: ''

Return

(void)

Source

function register_widget_control($name, $control_callback, $width = '', $height = '') {
	_deprecated_function( __FUNCTION__, '2.8', 'wp_register_widget_control()' );
	// Compat
	if ( is_array($name) ) {
		if ( count($name) == 3 )
			$name = sprintf($name[0], $name[2]);
		else
			$name = $name[0];
	}

	$id = sanitize_title($name);
	$options = array();
	if ( !empty($width) )
		$options['width'] = $width;
	if ( !empty($height) )
		$options['height'] = $height;
	$params = array_slice(func_get_args(), 4);
	$args = array($id, $name, $control_callback, $options);
	if ( !empty($params) )
		$args = array_merge($args, $params);

	call_user_func_array('wp_register_widget_control', $args);
}
WP Trac GitHub

Link here