title: Prototype - click event by element class name
body: <p>I am new to the prototype framework and am trying something really simple and failing.  I am trying to respond to a click event on a button like so:</p>
  
  <pre><code>$$('.btn').observe('click', respond);
  function respond(event) {
      alert("hello");
  }
  </code></pre>
  
  <p>Why isn't this working? Please help!</p>