From what I can see there is no way to pass along CSS classes to add to a form field. For example I wanted to add some space below a TEXT field and I can't, for I simply had to add a custom CSS rule targeted to that field. Being able to pass ipsSpacer_bottom directly would have saved me the trouble though.

And in case a custom theme has a different spacing compared to the default skin the change would automatically apply passing the CSS class, in my case I'll have to update my CSS rule for that theme instead. That's just an example with padding/margins, but it applies to anything really.

I have raised your suggestion internally with the team, thanks!