Continuation-style programming: are there constraints on the fx callbacks?

Continuation-style programming: are there constraints on the fx callbacks?

The documentation on e.g. the fadeIn() method does not specify any constraints on the callback argument.  Does that mean that 'anything will work'?  Specifically, is recursion allowed?

<edited>
Note that I'm not asking for empirical proof or suggestions on how to find out.  I want to know whether jQuery design has deliberately taken this into account.  Yes, I can read the source code.  No I don't plan to do so (for now), since I consider it an essential gap in the documentation.
</edited>

Example (taken from question on StackOverflow): 

function keep_animating(){
   $
("#id").fadeIn(500).fadeOut(500, keep_animating );
}