CGI::Struct lets you transform CGI data keys that _look like_ perl data
structures into _actual_ perl data structures.

CGI::Struct makes no attempt to actually _read in_ the variables from the
request. You should be using the CGI manpage or some equivalent for that.
CGI::Struct expects to be handed a reference to a hash containing all the
keys/values you care about. The common way is to use something like
'CGI->Vars' or (as the author does) 'Plack::Request->parameters->mixed'.

Whatever you use should give you a hash mapping the request variable names
(keys) to the values sent in by the users (values). Any of the major CGIish
modules will have such a method; consult the documentation for yours if you
don't know it offhand.