Jérôme Lafréchoux

Yes. Adding a link to the doc section you just added that should be reworded when dealing with this: https://github.com/marshmallow-code/marshmallow/pull/1774/files.

The alternative, to avoid breaking the update case, would be to document it as not thread-safe and invite the users to use a class rather than an instance, as this...

See discussion in #1791. It might be better not to merge this (breaking change) and instead perhaps raise a warning about the thread-safety issue.

Do you mean deprecate in 2.X and remove in 3 or deprecate in 3? Here are a few differences: - [Partial data if an item fails validation](https://github.com/marshmallow-code/marshmallow/issues/766) [#766] (Fixed in...

Yep, I just updated [the list above](https://github.com/marshmallow-code/marshmallow/issues/779#issuecomment-393283257).

@rooterkyberian, I was just searching for this thread to reference your issue.

All differences listed above are either fixed or on their way to be fixed. Once this is done, we should be able to deprecate `Nested(many=True)`.

Thans @0xpsilocybe, I think this is the object of [@sloria's comment](https://github.com/marshmallow-code/marshmallow/pull/1066#issuecomment-449638943) in #1066. I shall update the PR to propagate all needed `kwargs` to Nested.

@fuhrysteve, about this, please see the conversation in https://github.com/marshmallow-code/marshmallow/issues/928.

Indeed, deprecation can be done in 3.x so it doesn't have to hold 3.0. I sent https://github.com/marshmallow-code/marshmallow/pull/1290 with a fix for that last `List(Nested(...))` glitch we identified above (https://github.com/marshmallow-code/marshmallow/issues/779#issuecomment-396354987).