[plt-scheme] What are the semantics of optional variables?

If I may join Circular function in asking annoying questions (co-sinning as
it were), what exactly are the semantics of optional variables?
It appears from experiment that they are evaluated sequentially in
environments containing the previously declared parameters, kind of like
let*.
In fact, it appears that evaluation of optional parameters can safely[*]
mutate earlier optional and non-optional parameters.


[*] but not necessarily sanely.  I've probably been writing too much R code
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/users/archive/attachments/20080626/e3e01afa/attachment.html>