It works for me if you change $+ (last bracket) to $& (entire matched string). I assume $+ doesn't work because of the ?: clustering? My (simplified--on windows at the moment w/o Regex::Common) code/output is below. 
use Data::Dumper;
use strict;
use warnings;

use constant SUCCEED => qr{(?=)};
use constant FAIL    => qr{(?!)};

my $QUOTED = qr/".+?"/;
my $NUM = qr/\d*\.\d*/;

my $VALUE  = do {
    use re 'eval';
    qr/(?:$QUOTED|$NUM)(??{'.' eq $& ? FAIL : SUCCEED})/;
};

my $text = 'name => "foo", fav.num => 3.123';
my @text = split /($VALUE)/ => $text;
print Dumper \@text;

__END__

C:\temp>perl re.pl
$VAR1 = [
          'name => ',
          '"foo"',
          ', fav.num => ',
          '3.123'
        ];

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In reply to Re: Forcing a regex to fail by davidrw
in thread Forcing a regex to fail by Ovid

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