public function setMinChoices($minChoices)
    {
        if (is_int($minChoices) === true && $minChoices >= 0) {
            $this->minChoices = $minChoices;
        } else {
            $msg = "The 'minChoices' argument must be a positive integer, '" . gettype($minChoices) . "' given.";
            throw new InvalidArgumentException($msg);
        }
    }