title: find() and attr() in prototypejs
body: <p>What are equivalent of jQuery function find() and attr() in prototypejs?</p>
  
  <p>Could someone help me to convert this code using prototypejs?</p>
  
  <pre><code>var className = $(this).find('.myBtn').attr('class');
  $(this).find('.tab').attr('class', className + ' current');
  </code></pre>
  
  <p>Thanks in advance!</p>