[phpesp-general] What's UserID Used For??

[Alnisa A. <all...@gm...>]

I'm trying to make sure I have a good understanding of phpESP forms.
So I've been going through and checking what the various hidden input
values do, but I'm stuck at this one:

<input type=3D"hidden" name=3D"userid" value=3D"">

I know that sid stores the surveyid which is used in the primary
response table and related to response_id. I know that rid equals the
response_id which is used to relate questions to the response and
hence the survey. And of course sec is used to forward the user
through the various sections.

But I can't seem to find a value/use for userid. Is it used in the
authentication process? It seems to store the users IP address. But if
any value is pages via the url such as ?p=3D4 it will then store p=3D4 as
the userid instead of the users IP.

Can anyone give me an overview of what the userid does?

Alnisa