[plt-scheme] rest-like keyword arguments

Hi, I guess I was one of the few people who actually used pre-400's
keyword library. In the document describing the changes in v4, I see
the following:

http://pre.plt-scheme.org/plt/doc/release-notes/mzscheme/MzScheme_4.txt
>   "Rest"
>   arguments, such as the `x' in `(lambda x 10)', do not capture
>   keyword-based arguments; keyword arguments are completely separate
>   from by-position arguments, and a separate "rest"-like facility is
>   provided for accepting all provided keyword arguments.

Where can I find this rest-like facility for keyword arguments? I
don't see any mention of it at
http://pre.plt-scheme.org/docs/html/reference/lambda.html .

    Henk