Report which key or value caused the narrow to fail

[ssangervasi]

It can be tricky to develop a narrow schema for a large JSON, especially one that has optional keys. It would be helpful if when narrow returns false there was a way to find out which type comparison failed. I'd mainly use this while debugging, but there may be other runtime use cases.

(Example: I've run into this a bunch while parsing RSS feeds)

[ssangervasi]

I have a branch where I've tried creating a whole generic traverse & object diff algorithm. A thorough nested diff would be great, but so far the complexity is maybe not worth it.