Edit in JSFiddle

/* javascript pane is actually empty
   see HTML or just play to see the result */
<a href="#">link 1</a>

<a href="#">link 2</a>

<a href="#">link 3</a>

<div tabindex=0>tabindex=0 (natural order)</div>

<a href="#">link 4</a>

<a href="#" tabindex=-1>link with tabindex -1 (cannot tab)</a>