Overtrue\Validation\Validator::callExtension PHP Method

    protected function callExtension($rule, $parameters)
    {
        $callback = $this->extensions[$rule];
        if ($callback instanceof Closure) {
            return call_user_func_array($callback, $parameters);
        } elseif (is_string($callback)) {
            return $this->callClassBasedExtension($callback, $parameters);
        }
    }