package A;
sub new { bless {}, shift }
sub x { "A::x"; }
package B;
our @ISA="A";
package C;
our @ISA='A';
sub x{ shift->SUPER::x . " C::x" }
package main;
print A->new->x, "\n";
print B->new->x, "\n";
print C->new->x, "\n";
[download]

here is a example. see also perldoc perlboot.