WP_REST_Menu_Items_Controller::get_schema_links()

	protected function get_schema_links() {
		$links   = parent::get_schema_links();
		$href    = rest_url( "{$this->namespace}/{$this->rest_base}/{id}" );
		$links[] = array(
			'rel'          => 'https://api.w.org/menu-item-object',
			'title'        => __( 'Get linked object.' ),
			'href'         => $href,
			'targetSchema' => array(
				'type'       => 'object',
				'properties' => array(
					'object' => array(
						'type' => 'integer',
					),
				),
			),
		);

		return $links;
	}