$ perl -le'print __PACKAGE__'
main

##</code><code>##

$ perl -le'print CORE::__PACKAGE__'
main

##</code><code>##

$ perl -wle'BEGIN { *CORE::GLOBAL::__PACKAGE__ = sub () { "abc" }; } print __PACKAGE__'
abc

##</code><code>##

$ perl -wle'print prototype "CORE::__PACKAGE__"'
Can't find an opnumber for "__PACKAGE__" at -e line 1.