Win8 Strawberry 5.8.9.5 (32)  Thu 04/15/2021  1:56:15
C:\@Work\Perl\monks
>perl

use strict;
use warnings;

use Test::More 'tests' => 2;
1..2
use Test::NoWarnings;

my $rqr =   qr/\.(?:txt|png)$/i;  # regex as Regexp object
my $rsq = '(?i)\.(?:txt|png)$';   # regex as single-quoted string

my @Inputs = qw(
    x.txt .txt x.png .png x.TxT .tXt x.pNg .PnG
    txt png .txtx .pngx foo xtxtx
    );

my @mqr = grep { $_ =~ $rqr } @Inputs;  # matches from qr regex
my @msq = grep { $_ =~ $rsq } @Inputs;  # matches from '' regex

print "qr matches: @mqr \n";

is_deeply \@mqr, \@msq, 'qr// vs q//';

^Z
qr matches: x.txt .txt x.png .png x.TxT .tXt x.pNg .PnG
ok 1 - qr// vs q//
ok 2 - no warnings