first of all, thanks a million, I really appreciate the effort. this was the number one in my todo for this project, but I never had a chance to implement it for real.

for this particular change I have a comment: could you please update this example, so it's more clear that the number in square brackets is the index of an element which doesn't match with the schema (frankly, I didn't get this point before I looked at the corresponding part of the code). For example create an example where there're more elements or something...

Also it probably would be good to have some mention that this is the path, so it's easier to spot it. for example it could be a tuple like {path, [...]} or even {data_path, [...]}, or path_in_data :) I'm open to discuss it.