Order_History::render( $attr,  $instance )

	public function render( $attr, $instance ) {
		if ( ! is_user_logged_in() ) {
			return '';
		}

		$attr             = shortcode_atts( self::default_attributes(), $attr, self::NAME );
		$attr['per_page'] = $attr['per_page'] ?: $this->per_page_default();

		if ( empty( $_GET[ self::ORDER_ID_QUERY_ARG ] ) ) {
			return $this->render_history_list( $attr );
		} else {
			return $this->render_order_details( $attr, (int) $_GET[ self::ORDER_ID_QUERY_ARG ] );
		}

	}