What are valid Perl module return values?

Question

The common practice in Perl is of course to end modules with 1; so that a call to require can then be checked for success. Is there any reason that the return

Answer 1

Mark Dominus, author of Higher-Order Perl, explains my favorite:

I have very rarely used $flag = 'Cogito ergo sum'; which as everyone knows is self-evidently true in all possible universes. This ensures maximum portability.