public function find($re, $filter = null) {
        $result = null;
        $this->each(function($context) use ($re, $filter, &$result) {
            $r = $context->find($re, $filter);
            if (!$r->isEmpty()) {
                $result = $r;
                return false;
            }
        });

        return $result?:Context::getEmptyContext();
    }