#---------------------------------------------------------
# Foo_1.pm
use strict;
use warnings;
package Foo;

my $HELLO='elloHay';
our $GOODBYE ='oodbyeGay';
sub hello { "hi! $HELLO -> $GOODBYE"; }
1;

#---------------------------------------------------------
# Foo_2.pm
use strict;
use warnings;
package Foo;

# You are right Tilly - "our" doesn't reset $GOODBYE
# and strict won't complain about an unqualified our
# variable so long as we declare it

our $GOODBYE;
print "GOODBYE=$GOODBYE\n";
# no compiler complaints from above line
# outputs:  GOODBYE=oodbyeGay

$Foo::HELLO='Bonjour';       #this is OK
$Foo::GOODBYE='Au revoir';   #this is OK
print hello() . "Hello=$Foo::HELLO, Goodbye=$Foo::GOODBYE\n";

# in the hello() sub HELLO and GOODBYE are both unqualified.
# the my variable(HELLO) retains its old value, but the our
# variable (GOODBYE) reflects the new value because with
# or without qualification it is global (in the package table)

#outputs:
hi! elloHay -> Au revoir: Hello=Bonjour Goodbye=Au revoir
#NOT
hi! elloHay -> oodbyeGay: Hello=Bonjour Goodbye=Au revoir
#NOR
hi! Bonjour -> Au revoir: Hello=Bonjour Goodbye=Au revoir