Source

File: wp-includes/widgets/class-wp-widget-rss.php

public function __construct() {
		$widget_ops  = array(
			'description'                 => __( 'Entries from any RSS or Atom feed.' ),
			'customize_selective_refresh' => true,
		);
		$control_ops = array(
			'width'  => 400,
			'height' => 200,
		);
		parent::__construct( 'rss', __( 'RSS' ), $widget_ops, $control_ops );
	}