It's a wrapper for Flickr::API, and a base class for other Flickr related libraries, that does two things, principally :

* Throttling of API calls

* Test API responses for errors and to return objects that can be queried using XPath rather than the freakish moon-language tree/hash objects that Cal favours.

It also sets up logging facilities and handles a couple other mundane tasks that you need to do when using the Flickr API.