http://www.perlmonks.org?node_id=886319


in reply to Re^5: how ! operator works
in thread how ! operator works

My answer is more or less an educated guess. If you want to look around to confirm or for fun, PL_sv_no is the SV returned when a builtin wants to return something false. An interesting puzzle would be to see if you can manage to lower the refcount and display it at the lower refcount using Devel::Peek's Dump.