My code is working well enough -- but I don't understand the results. My goal is to make sure that the value passed in is in one of these formats:

* 00000-0000
* 000000000
* 00000

PHP:

```
$str = '12345-6789';
preg_match('/^[0-9]{5}(-?[0-9]{4})?$/', $str, $found);
print_r($found);

```

Return:

```
Array
(
    [0] => 12345-6789
    [1] => -6789
)

```

Why am I getting the second result, `[1] => -6789`?

Thanks!