[Seaside] Scriptaculous example of SUEvaluator ?

[Florian Minjat]

Hi,
   I am trying to do a form with validators and confirmation in ajax. 
All the validation need to be done server-side. My problem is to do 
something like this in a onClick statement :
      isFormValid ifTrue: [html updater id: 'formDivId'; callback: [:r 
| self renderValidFormOn: r]
   But I need to evaluate isFormValid server-side with an Ajax request 
because it will only be set as true when the form is validate by ajax. 
So currently this updater never shows up.
   I think I could use the SUEvaluator, but couldn't find any example. 
So I don't really know how to use it.
   Does somebody know how to do that using as much seaside as 
possible? And can somebody give me an example of SUEvaluator?

Florian