The modifications to `__setitem__` are specific to the classes that derive from here, but the `update` is a generic implementation.

Want me to add the below here to make it clear that this is an abstract class and that `__setitem__` should de redefined in order to use this?

```python
def __setitem__(self, *args, **kwargs):
    "Abstract __setitem__ method, should be redefined in subclasses of DictObject."""
    raise NotImplementedError
```