As I said at RubyConf 2010, I'd like to propose a new features called "Refinements." Refinements are similar to Classboxes. However, Refinements doesn't support local rebinding as mentioned later. In this sense, Refinements might be more similar to selector namespaces, but I'm not sure because I have never seen any implementation of selector namespaces. In Refinements, a Ruby module is used as a n