title: How to get the index of the previous/next non-disabled option (relative to the selected option)?
body: <p>Please, take a look at this:</p>
  
  <pre><code>&lt;select&gt;
    &lt;optgroup label="Group 1"&gt;
      &lt;option&gt;1.1
      &lt;option&gt;Get my index (1)!
      &lt;option disabled&gt;1.3
    &lt;optgroup label="Group 2"&gt;
      &lt;option selected&gt;I am selected
      &lt;option disabled&gt;2.2
    &lt;optgroup label="Group 3"&gt;
      &lt;option disabled&gt;3.1
      &lt;option&gt;Get my index (6)!
      &lt;option&gt;3.3
  &lt;/select&gt;
  
  &lt;script&gt;
      var sIndex = $("select").prop("selectedIndex");
      var nextClosestIndex = $("select").find("option").filter(function (i) {
          return $(this).prop("disabled") === false &amp;&amp; this.index &gt; sIndex
      }).prop("index");
      alert(nextClosestIndex + ', which is right by accident, but I strongly dislike this way');
      var prevClosestIndex = "I have no idea how to get 1";
      alert(prevClosestIndex);
  &lt;/script&gt;
  </code></pre>
  
  <p>(end tags are omitted as in HTML5 spec, it makes no difference).<br>
  I think you can see the problem: I'm trying to get those indices, but can't find the way.</p>