Here is some (very slightly modified) code directly from the NEXT module perldoc. Note I commented out sub foo in package E:

    package A;                 
    sub foo { print "called A::foo\n"; shift->NEXT::UNSEEN::foo() }

    package B;                 
    sub foo { print "called B::foo\n"; shift->NEXT::UNSEEN::foo() }

    package C; 
    use vars qw( @ISA );
    @ISA = qw( A );
    sub foo { print "called C::foo\n"; shift->NEXT::UNSEEN::foo() }

    package D; 
    use vars qw( @ISA );
    @ISA = qw(A B);
    sub foo { print "called D::foo\n"; shift->NEXT::UNSEEN::foo() }

    package E; 
    use vars qw( @ISA );
    @ISA = qw(C D);
    #sub foo { print "called E::foo\n"; shift->NEXT::UNSEEN::foo() }

package ::;

E->foo();
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And here is its output:

called C::foo
called A::foo
called D::foo
called B::foo

Now, here is my code that does almost the exact same thing:

#!/usr/local/bin/perl
use NEXT;
use strict;

package ROOT;
sub traverse { print __PACKAGE__, "\n"; }

package LEFT_CHILD;
#use base 'ROOT';
use vars qw( @ISA );
@ISA = qw( ROOT );
sub traverse {
    my $package = shift;
    print __PACKAGE__, "\n";
    $package->NEXT::UNSEEN::traverse();
}

package RIGHT_CHILD;
#use base 'ROOT';
use vars qw( @ISA );
@ISA = qw( ROOT );
sub traverse {
    my $package = shift;
    print __PACKAGE__, "\n";
    $package->NEXT::UNSEEN::traverse();
}

package GRANDCHILD;
#use base 'LEFT_CHILD';
#use base 'RIGHT_CHILD';
use vars qw( @ISA );
@ISA = qw( LEFT_CHILD RIGHT_CHILD );

package ::;

GRANDCHILD->traverse();
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Here is the output:

LEFT_CHILD
ROOT

Nodes relating to XP: