[plt-scheme] How to scribble optional arguments in defproc?

Grant Rettke wrote:
> What is the "right way"to define optional arguments in @defproc statements?
>
> I have been using (optional ...) so far.
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In @defproc, arguments are automatically formatted as optional when the 
scribbled definition includes a default value, as well as the id and 
contract.

For @defparam and @defboolparam, the default values need to be described 
in the prose section.

Yavuz