title: Event.observe function - observe element by class instead of id
body: <p>There is prototype js function:</p>
  
  <p><em>Event.observe(element, eventName, handler)</em></p>
  
  <p>here the <strong>element</strong> means element's ID.</p>
  
  <p>Is it possible to put here element's <strong>class</strong>?</p>
  
  <p>I got this element from third party with class attribute only.</p>