Custom state key for switch transition

[yemi]

Hi and thanks for this lib!

I have a question, where would I look in order to support using a certain key on the state that, when changed should trigger a transition?

The reason is that the state object might change but if it's e.g. object.id is the same, it shouldn't transition.

I would be happy to look in to the source code, but it you know straight away where to look to implement this, I'd be happy :)