$ perl -Mstrict -Mwarnings -E'package main; say __PACKAGE__'
main
$ perl -Mstrict -Mwarnings -E'package ::main; say __PACKAGE__'
main
$ perl -Mstrict -Mwarnings -E'package ::; say __PACKAGE__'
::
$ perl -Mstrict -Mwarnings -E'package ::::; say __PACKAGE__'
::::