title: body background-image change with fade effect mootools
body: <p>I'm changing my background-image css property using Mootools:</p>
  
  <p><strong>$(document.body).setStyle('background-image','url(' + pBackground + ')');</strong></p>
  
  <p><em>And it's its working, but how can a make one fade effect between picture change?</em></p>
  
  <p>Thanks,
  Pedro</p>