(In the proposed equality comparison of undef values) I would expect true only when both values are undef, false in any other case. That would result in much, w.r.t. Perl 5, POLA violation when warnings are off, namely 0 == undef and '' eq undef both returning false of course.

One third day later ... Near "POLA violation" added the warnings usage, and corrected the given comparison results (in Perl 5 without warnings, results are true values).