Example uses are:
- rows in a table
- menu items
- fieldsets in a form
This extension will, when applied to a set of elements, map their vertical position on the page. Then, when you press the UP and DOWN arrow keys, it will set a focused class and optionally trigger the focus event on the next of the mapped elements, in the order they were mapped. You can update the mapping at any time (e.g. when you add new elements to the DOM).
Released to the public domain: The Unlicense