Nette\Forms\Controls\MultiSelectBox::setItems PHP Method

    public function setItems(array $items, $useKeys = TRUE)
    {
        if (!$useKeys) {
            $res = [];
            foreach ($items as $key => $value) {
                unset($items[$key]);
                if (is_array($value)) {
                    foreach ($value as $val) {
                        $res[$key][(string) $val] = $val;
                    }
                } else {
                    $res[(string) $value] = $value;
                }
            }
            $items = $res;
        }
        $this->options = $items;
        return parent::setItems(Nette\Utils\Arrays::flatten($items, TRUE));
    }