protected function selectors(&$out)
    {
        $s = $this->seek();
        $selectors = [];

        while ($this->selector($sel)) {
            $selectors[] = $sel;

            if (! $this->literal(',')) {
                break;
            }

            while ($this->literal(',')) {
                ; // ignore extra
            }
        }

        if (count($selectors) === 0) {
            $this->seek($s);

            return false;
        }

        $out = $selectors;

        return true;
    }