protected function expression(&$out)
    {
        if ($this->value($lhs)) {
            $out = $this->expHelper($lhs, 0);

            // look for / shorthand
            if (!empty($this->env->supressedDivision)) {
                unset($this->env->supressedDivision);
                $s = $this->seek();
                if ($this->literal('/') && $this->value($rhs)) {
                    $out = array('list', '',
                        array($out, array('keyword', '/'), $rhs), );
                } else {
                    $this->seek($s);
                }
            }

            return true;
        }

        return false;
    }