As noted in PHPC-712, we encountered an edge case where a libmongoc API we were using for bulk writes did not validate a document before storage. This allowed users to store a document (via an insert or update/replace) containing a dotted field name.

I understand that drivers should test for this before sending writes over the wire, but I would have expected the server to also validate a document before storage. Based on my testing, server versions from 2.4 through 3.2 do not complain about dotted field names.

I've also noted the edge case where dotted field names need to be allowed for legacy index creation (i.e. insertions to system.indexes).