use strict;
package First;

our $foo = 42;

{
   print $foo; # 42

   package Second;

   print $foo; # 42, refers to $First::foo

   our $bar = 54;

   {
       package Third;
       print $foo;  # 42, refers to $First::foo
       print $bar;  # 54, refers to $Second::bar
   }
}

print $Second::bar; # 54, fully qualified.
print $bar;         # error: not strict-safe as the our is not in scope.