Currently here (for invalid data to parse_obj) and here (in parse_raw) we use '__obj__' as the location for errors to indicate an error which is general to the model, not specific to a field.

We should change this in v1 to __root__ to better match other nomenclature, eg. custom root types, where we use __root__.

We should also implement at some point entire model validation, as discussed at #691 (comment). I guess to match the above naming, we should do this using a special value to a validator @validator('__root__'). If this raised an error it would end up in ValidationError details with 'location': '__root__', (Unless it's a "@validator('__root__')" validator for a submodel, when obviously it should have the location of that model.

Perhaps it would would be nice to have a special decorator @root_validator which is an alias of @validator('__root__'), we should support multiple root validators either as a result of inheritance or on a single class.

I guess the __obj__ > __root__ change must happen with v1 and the new root validator could go in a later release, but we should be sure we won't need other backwards incompatible changes to implement the root validator.

Thoughts?