`class_attribute` is required anyway to work with inheritence. As you can see all datagrid dsl config (scope, filters, columns)  is stored like this by the same reason.

Also all Rails dsl is going with `self.option = value` DSL. I am not 100% agree with that. But it became a standard in activerecord. Maybe because of `class_attribute` impact that stores a lot of wisdom about Ruby crap class ivars model. https://github.com/rails/rails/blob/master/activesupport/lib/active_support/core_ext/class/attribute.rb#L71

I still prefer `class_attribute`.