c:\@Work\Perl>perl -le
"use warnings;
 use strict;
 ;;
 print qq{Perl ver.: Strawberry $]};
 ;;
 package XX {
   use constant to_1 =>  42;
   use constant to_2 => 999;
   }
 ;;
 package YY {
   use parent -norequire, 'XX';
   use constant to_2 => 137;
   }
 ;;
 my $y = bless {} => 'YY';
 ;;
 print $y->to_1;
 print $y->to_2;
 ;;
 print YY->to_1;
 print YY->to_2;
 ;;
 print XX::to_1;
 print XX::to_2;
 print YY::to_2;
 ;;
 print YY::to_1;
"
Name "YY::to_1" used only once: possible typo at -e line 1.
Perl ver.: Strawberry 5.014004
42
137
42
137
42
999
137
print() on unopened filehandle to_1 at -e line 1.