[plt-scheme] scribble #<void>

If I put some scheme code in a .scrbl file I end up with #<void>'s 
printed in the result (I was hacking 
scribblings/reference/file-ports.scrbl). How can I avoid printing #<void> ?

I have something like
@(begin
      ..stuff..)

(define ...) doesn't seem to print anything so I could just wrap all 
expressions with a (define xxx ...).