There is currently no way of controlling what the insert/update functions check for when validating BSON documents prior to insert/update. For example, a client can not ask the validation function called by mongoc_collection_update() to validate the BSON and tell it to allow empty keys. This can of course be worked around by explicitly calling bson_validate() with the desired flags and then calling insert/update with MONGOC_INSERT/UPDATE_NO_VALIDATE set, but that adds a little bit of complexity and some code clutter to client code. It would be handy to just be able to pass bson_validate_flags_t to the insert/update calls.