title: Changing TR class does not seem to work
body: <p>I'm trying to change the TR className with javascript, why it doesn't seem to work (note : must work also for IE8)</p>
  
  <pre><code>&lt;html&gt;
  &lt;head&gt;
    &lt;style&gt;
      tr.test {background-color:#000000;margin:0;border:0;padding:0;}
    &lt;/style&gt;
    &lt;script&gt;
    _table = document.getElementsByTagName("table")[0];
    _tbody = _table.getElementsByTagName("tbody")[0];
    _tr = _tbody.getElementsByTagName("tr")[0];
    _tr.className="test";
    &lt;/script&gt;
  &lt;/head&gt;
  &lt;table&gt;
    &lt;tbody&gt;
      &lt;tr&gt;
      &lt;td&gt;&lt;/td&gt;
      &lt;/tr&gt;    
    &lt;/tbody&gt;
  
  &lt;/table&gt;
  &lt;/html&gt;
  </code></pre>