Open
Description
As indicated in #452, there are some issues with FrozenClass.
The allowed attributes are a class attribute of FrozenClass and are therefore shared across all derived classes. For example, you add error_embedded_estimate to the status class of level and then you can set error_embedded_estimate for the status of the step as well. It's not nice. It doesn't really enforce what the frozen classes are about. I am sure there is a simple solution for this that I am just not able to see at the moment.