Instead of using tab to navigate through elements on this page, try using + on the keypad. Also try reverse navigation with shift-+.
In this demo, most of the elements are plussable, but the normal use case is to enable plussing where users input mostly numbers (as in quantities, zip codes, short date formats) using the keypad. The normal tab key still works as usual.
Laptops may not have physical keypads, but instead it is emulated with the Fn key (or similar). PlusAsTab is not targeted at laptop users. It is possible to use an external/separate USB keypad though. Perhaps laptop users would be more interested in the PlusAsTab demo that uses enter as tab? The key is configurable, and multiple keys are supported - read more on the project page.