Que é o que está no código que você postou:
/ Brands regex
$brands = array(
'visa' => '/^4\d{12}(\d{3})?$/',
'mastercard' => '/^(5[1-5]\d{4}|677189)\d{10}$/',
'diners' => '/^3(0[0-5]|[68]\d)\d{11}$/',
'discover' => '/^6(?:011|5[0-9]{2})[0-9]{12}$/',
'elo' => '/^((((636368)|(438935)|(504175)|(451416)|(636297))\d{0,10})|((5067)|(4576)|(4011))\d{0,12})$/',
'amex' => '/^3[47]\d{13}$/',
'jcb' => '/^(?:2131|1800|35\d{3})\d{11}$/',
'aura' => '/^(5078\d{2})(\d{2})(\d{11})$/',
'hipercard' => '/^(606282\d{10}(\d{3})?)|(3841\d{15})$/',
'maestro' => '/^(?:5[0678]\d\d|6304|6390|67\d\d)\d{8,15}$/',