How Can I Make List Items "Tabbable" (Use Tab Key To :focus On Them)

How can I make List Items tabbable? (meaning: using the TAB key to :focus on them). I need to know for Handicap Accessibility purposes.

jsFiddle attached, I added 2 text fields to give a point to TAB from; if you tab from the textarea it goes to the next one, then skips over all the list items.

jsFiddle: https://jsfiddle.net/h815zLnp/