package a;
sub method {
 my $self=shift;
 # do something
}

package b;
use NEXT;
sub method {
 my $self=shift;
 # do something before
 $self->NEXT::method(@_); # do the normal stuff
 # do something after
}

package main;
require a;require b;
use Merge qw(b a)=>'c';

$c=new c;$c->method; # will call "b"'s implemetation, which will call "a"'s via NEXT