Does this mean that the user should be calling `resource.custom_data.save()` after having called `del` on the custom data? If so, please specify in the sample code.

Another question: is the custom data operation (update or delete) sent to the server when the `save` method is called on the resource (as opposed to calling it on the custom data)? 
For example, would the following code update the custom data?:

```python
 account.custom_data['rank'] = 'Captain'
 account.save()

 del account.custom_data['rank']
 account.save()

The SDK should be able to work this way since the REST API allows the user to save the custom data from the resource endpoint (and other SDKs too).