Sometimes it may be useful to not specify a prefix to the path. In my special situation i want to load models with the PluginLoader and I want to follow restrictions made for the Controller, so the Models are name like "Module_BarModel", but for the default-Module it will only called "FooModel". If an empty string is given as prefix _formatPrefix will ever append an underscore

    protected function _formatPrefix($prefix)
    {
        return rtrim($prefix, '_') . '_';
    }

So, if i try to loader "FooModel", it will (at least) search for "_FooModel". It seems to be more useful, if empty strings as prefix will stay empty strings.

    protected function _formatPrefix($prefix)
    {
        return !empty($prefix) ? rtrim($prefix, '_') . '_' : '';
    }