public function addExpression($name, $expression)
    {
        if (!is_array($expression)) {
            $expression = ['expr' => $expression];
        } elseif (isset($expression[0])) {
            $expression['expr'] = $expression[0];
            unset($expression[0]);
        }

        $c = $this->_default_seed_addExpression;

        return $this->add($this->factory($c, $expression), $name);
    }