What is false in Perl

WhatIsFalse.pl

use feature qw(say);
use warnings;

my $false = !1;
say defined $false; # 1

say '----';

say '!1 is false' unless $false;        # !1 is false
say '0 is false' unless 0;              # 0 is false
say '0.00 is false' unless 0.00;        # 0.00 is false

say '0x0 is false' unless 0x0;          # 0x0 is false
say '0e0 is false' unless 0e0;          # 0e0 is false
say '"0" is false' unless "0";          # "0" is false

say '3-2-1 is false' unless 3-2-1;      # 3-2-1 is false
say 'sin(0) is false' unless sin(0);    # sin(0) is false
say '"0" is false' unless "0";          # "0" is false

say '"0.00" is false' unless "0.00";    # returns nothing
say '0x0 is false' unless "0x0";        # returns nothing
say '0e0 is false' unless "0e0";        # returns nothing

say '3-2-1 is false' unless '3-2-1';    # returns nothing
say 'sin(0) is false' unless 'sin(0)';  # returns nothing

say '"" is false' unless "";            # "" is false
say '() is false' unless( () );         # () is false
say 'undef is false' unless undef;      # undef is false