Trace back to where $self was defined, and the hash key YYYY. You say "no use modules", but (excuse me if you already know this) modules can also be included using require or the -M command-line option and a few other screwy ways, like export_fail and autoload.

If they have set @ISA = qw(Exporter) then that looks like the code you are looking at is inside a module already, otherwise why export?