#!/usr/bin/perl
use strict;
use warnings;
use utf8;
use Unicode::Normalize;
use charnames ':full';
my $str = 'Ä';

sub mydump {
    print map { '\N['. charnames::viacode(ord $_) . ']' } 
                split m//, $_[0];
    print "\n";
}

mydump $str;
mydump NFKD($str);
mydump scalar reverse NFKD($str);

binmode STDOUT, ':utf8';
my $tmp = "\nÄO";
print scalar reverse NFKD($tmp);
__END__
\N[LATIN CAPITAL LETTER A WITH DIAERESIS]
\N[LATIN CAPITAL LETTER A]\N[COMBINING DIAERESIS]
\N[COMBINING DIAERESIS]\N[LATIN CAPITAL LETTER A]
ÖA