title: Why would an `a` tag need `tabindex=0`?
body: <p>I'm working on a web app, and one of the repeated <code>a</code> (anchor) elements does not get keyboard focus as I tab through the page. Only if I add <code>tabindex=0</code> can I tab to it.</p>
  
  <p>(Although my goal is to make the focus visible, I'm determining whether an element gets focus by using a snippet of jQuery:</p>
  
  <pre><code>// Whenever I hit tab, show me which element has focus
  $('main').on('keydown',function(e) { 
    var keyCode = e.keyCode || e.which; 
  
    if (keyCode == 9) { 
      console.log("focus is now on ", $(':focus'));
    } 
  });
  </code></pre>
  
  <p>)</p>
  
  <p>This confuses me. According to <a href="http://www.w3.org/html/wg/drafts/html/master/dom.html#interactive-content" rel="noreferrer">the specs</a>, "The tabindex attribute can also make any element into interactive content" - but <code>a</code> is one of the ones they list as interactive by default.</p>
  
  <p>And again, from an accessibility article:</p>
  
  <blockquote>
    <p>A [tabindex] value of 0 indicates that the element should be placed in the
    default navigation order. This allows elements that are <strong>not natively
    focusable</strong> (such as &lt;div&gt;, &lt;span&gt;, and &lt;p&gt;) to receive keyboard focus.
    Of course one should generally use links and form controls for all
    interactive elements...
    (<a href="http://webaim.org/techniques/keyboard/tabindex" rel="noreferrer">http://webaim.org/techniques/keyboard/tabindex</a>)</p>
  </blockquote>
  
  <p>What would cause an anchor element to be skipped as I tab through the interactive elements of a page?</p>