[WIP] Refactor docs

Fix #94.
It does indeed. The difference is that `latest` does not come from the request attributes (it’s hard-coded) and `id` does. They look the same because the InvalidationSubscriber *tries* to evaluate each parameter as an expression against request attributes, and fails silently when it doesn’t seem to be an expression (as in the case of `latest`). 

Do you have an idea as to how we could make this clearer? Should we make the behaviour more explicit?