title: How to add a custom validation to Magento prototype
body: <p>I want to make a simple url validator for some custom fields. I tried the default ones (adding the class <code>validate-url</code> or  <code>validate-clean-url</code> to the input) - but these don't work quite as I would like them to, so I want to write some of my own javascript, but integrated with the prototype validation.</p>
  
  <p>Does anyone have any ideas how I can do this?</p>
  
  <p>I didn't find anything helpful in my searches, and I am not very Prototype-savy (worked mostly with jQuery).</p>