use utf8;
use 5.14.0;

use Data::Dumper;
$Data::Dumper::Terse = 1;
$Data::Dumper::Indent = 0;

use Encode;

binmode STDOUT, ":encoding(utf-8)";

my $s = "ä"; 
my @res = (
        qr/\N{U+00e4}/, 
        qr/\N{U+00e4}+/, 
        qr/\xe4/, 
        qr/\xe4+/, 
        qr/[\N{U+00e4}]/, 
        qr/[\N{U+00e4}]+/, 
        qr/[\xe4]/, 
        qr/[\xe4]+/,
        qr/ä/,
        qr/ä+/,
        qr/[ä]/,
        qr/[ä]+/,
);

for my $re (@res) {

    my $m = ($s =~ $re) ? "true" : "false";
    printf "%s =~ %30s  == %s\n", $s, decode("UTF-8",Dumper($re)), $m;
}

##</code><code>##

~/perl5/perlbrew/perls/perl-5.16.0/bin/perl test.pl
ä =~           qr/(?^u:\N{U+00e4})/  == true
ä =~          qr/(?^u:\N{U+00e4}+)/  == true
ä =~                 qr/(?^u:\xe4)/  == true
ä =~                qr/(?^u:\xe4+)/  == true
ä =~         qr/(?^u:[\N{U+00e4}])/  == true
ä =~        qr/(?^u:[\N{U+00e4}]+)/  == false
ä =~               qr/(?^u:[\xe4])/  == true
ä =~              qr/(?^u:[\xe4]+)/  == true
ä =~                    qr/(?^u:ä)/  == true
ä =~                   qr/(?^u:ä+)/  == true
ä =~                  qr/(?^u:[ä])/  == true
ä =~                 qr/(?^u:[ä]+)/  == false