$regex = qr/foo/; # should return 0

##</code><code>##

sub captures {
    my $re = shift;
    return scalar ( @_ = '' =~ /(?:($re))?/ ) - 1;
}

##</code><code>##

 
$regex = qr/(?x)  # (comment)
            (?-x) # (capture) (?x) # (comment)/;