$keys = '';
$keys .= 'field' . 'A';
@keys = split /field/, $keys, -1; # grabs trailing zero-lengths
pop @keys;

##</code><code>##

use warnings;
use strict;

my @str = (
    'Value:',
    'Value:.',
    'Value:...',
    'Value:A',
    'Value:A.B',
    'Value:.A',
    'Value:A.',
);

for (@str){
    m/^ Value: \K (.*) $/x;
    my $keys = $1;
    my @keys;
    my $i = 0;
    @{ $keys[ $i ++ ] } = split /\./, $keys;
    @{ $keys[ $i ++ ] } = split /\./, $keys, -1;
    @{ $keys[ $i ++ ] } = $keys =~ m/\w*/g;
    @{ $keys[ $i ++ ] } = $keys =~ m/\w*?(?=\.|$)/g;
    
    my $keys_plus = $keys . '.A';
    @{ $keys[ $i ++ ] } = split /\./, $keys_plus, -1;
    pop @{ $keys[ $i - 1 ] };

    print "{$keys}:\n";
    for my $j (0 .. $i - 1){
        print map "<$_>\n", join '', map "[$_]", @{ $keys[ $j ] };
    }
    
    print "\n";
}

__END__
{}:
<>
<>
<[]>
<[]>
<[]>

{.}:
<>
<[][]>
<[][]>
<[][]>
<[][]>

{...}:
<>
<[][][][]>
<[][][][]>
<[][][][]>
<[][][][]>

{A}:
<[A]>
<[A]>
<[A][]>
<[A][]>
<[A]>

{A.B}:
<[A][B]>
<[A][B]>
<[A][][B][]>
<[A][][B][]>
<[A][B]>

{.A}:
<[][A]>
<[][A]>
<[][A][]>
<[][A][]>
<[][A]>

{A.}:
<[A]>
<[A][]>
<[A][][]>
<[A][][]>
<[A][]>