>perl
use strict;
use warnings;
my $stuff = undef;
BEGIN { $stuff = 1; }
print "$stuff\n";
^Z
1

>perl -MO=Deparse
use strict;
use warnings;
my $stuff = undef;
BEGIN { $stuff = 1; }
print "$stuff\n";
^Z
use warnings;
use strict 'refs';
my $stuff;
sub BEGIN {
    $stuff = 1;
}
print "$stuff\n";
- syntax OK

>perl
use strict;
use warnings;
my $stuff;
BEGIN { $stuff = 1; }
print "$stuff\n";
^Z
1