[plt-scheme] Scribble question

Hi there,

is there a standardized way to document in Scribble the R6RS type of
case-lambda optional parameters? Here is a concrete example:

(define token-sequence->ngrams
   (case-lambda
     [(tokens)   (token-sequence->ngrams tokens 2)]
     [(tokens n) (token-sequence->ngrams
                     tokens n
                     (make-hashtable equal-hash equal?))]
     [(tokens n ngrams)
      ...

How would you document such cases of optional parameters, with @defproc,
or in an alternative way? I can't find any example anywhere on the net?

I'd appreciate some hint or advice!

Thanks a lot and
best wishes
DC