There's a related thread here https://github.com/Jasonette/documentation/issues/32
I didn't have time to think too much into this yet because it's one of those "good to have" features but actually can potentially cause a lot of headaches in implementation.
While developing Jasonette I got burned by a lot of seemingly little useful features that ended up adding to complexity and caused a lot of unexpected bugs later, which is why I didn't invest too much time into this yet--it should be easy to implement but I am not yet sure of the side effects.
But I do think it would be useful and probably will try to revisit when I have more resources to do so in the future. In the meantime feel free to follow the github thread if you're interested in getting updates on this.