مثال:
use yii\base\Model;

class MyForm extends Model
{
public $country;
public $token;

public function rules()
{
return [
// an inline validator defined as the model method validateCountry()
['country', 'validateCountry', 'countries'=>['USA', 'Web']],

// an inline validator defined as an anonymous function
['token', function ($attribute, $params) {
if (!ctype_alnum($this->$attribute)) {
$this->addError($attribute, 'The token must contain letters or digits.');
}
}],
];
}

public function validateCountry($attribute, $params)
{
if (!in_array($this->$attribute, $params['countries'])) {
$this->addError($attribute, 'The country must be "' . implode('" or "', $params['countries']) . ".');
}
}
}