title: jQuery select by class VS select by attribute
body: <p>I want just to ask for an opinion of perfomance:
  Is it faster selecting elements by class name or by attribute name with jquery?
  Example I have 100 DIVs element in this form:</p>
  
  <pre><code>&lt;div class="normal_box" normal_box=1&gt;...&lt;/div&gt;
  </code></pre>
  
  <p>Which is faster:</p>
  
  <pre><code>$('div.normal_box').each(function(){...});
  </code></pre>
  
  <p>VS</p>
  
  <pre><code>$('div[normal_box=1]').each(function(){...});
  </code></pre>
  
  <p>I made some experiments on 30 divs but I don't see any difference with (new Date).getTime();
  Maybe selecting by class is more efficient on CPU usage?</p>