public function unregisterPlugin($plugin)
    {
        if (false !== strpos($plugin, '_')) {
            foreach ($this->_plugins as $key => $_plugin) {
                if ($plugin == get_class($_plugin)) {
                    unset($this->_plugins[$key]);
                }
            }
        } else {
            $plugin = strtolower($plugin);
            if (isset($this->_plugins[$plugin])) {
                unset($this->_plugins[$plugin]);
            }
        }
        return $this;
    }