how does craigslist do it?

how does craigslist do it?
for example
what does the following line do? (when posting a new ad)

<form action=/van/C/ats/none/x/tb9EeveRsqQpyxCx/8et79 method=post>

which script does this evoke?
is there some kind of alias set up?
or is there one huge script that handles all the POST data?
how can i set this up with perl?

cheers

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