Allowing sublayouts to control their own HTML cache keys

I spoke to a fellow MVP recently, Kern Herskind Nightingale and the topic of my blog came up, along with the fact that I hadn't (at the time) updated for a while. The reason was my previous post about overriding rendering types. Originally, I had intended to use an example that would allow developers to add an interface to their sublayout classes and specify custom logic around building their cache keys, but it didn't work as I'd intended.