public function addQuickSearch($fields, $options = null, $class = null, $spot = null)
    {
        // add only once
        // @todo decide, maybe we should destroy and recreate to keep last one
        if ($this->quick_search) {
            return $this->quick_search;
        }

        $this->quick_search = $this->add($class ?: $this->quick_search_class, $options, $spot ?: 'quick_search');
        /** @type QuickSearch $this->quick_search */
        $this->quick_search
            ->useWith($this)
            ->useFields($fields);

        return $this->quick_search;
    }