public function appendBody($content, $name = null)
    {
        if ((null === $name) || !is_string($name)) {
            if (isset($this->_body['default'])) {
                $this->_body['default'] .= (string) $content;
            } else {
                return $this->append('default', $content);
            }
        } elseif (isset($this->_body[$name])) {
            $this->_body[$name] .= (string) $content;
        } else {
            return $this->append($name, $content);
        }

        return $this;
    }