"...I didn't understand from here..."

I guess it's just because some of the elder fellow monks are a lazy bunch.

Consider this untested snippet or sketch - as you like:

#!/usr/bin/env perl

use strict;
use warnings;
use Data::Dump;
use feature qw (say);

my %HoA = (
    bar => ["13 : //comment thirteen"],
    foo => [ "12 : //comment twelve ", "5  : //comment five" ],
);

dd \%HoA;

say qq(\n--\n);

# like in "Perl Programming" AKA "Camel Book" chapter 9...
for my $key ( keys %HoA ) {
    say qq($key: );
    for my $item ( 0 .. $#{ $HoA{$key} } ) {
        say qq( $item = $HoA{$key}[$item]);
    }
    print qq(\n);
}

__END__
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Best regards, Karl