document recommendation for ValidationAction
@@ -35,6 +35,9 @@ Note that you do not need to implement the `name` method in the custom action ex
is already implemented. If you override the `name` method, the custom validation action will not run because the
original name is hardcoded in the call that the default action `action_extract_slots` makes to the action server.
+It is recommended to create only one subclass of `ValidationAction` which should contain all extraction and validation
+methods for different slots according to your use-case.
+
With this option, you do not need to specify the `action` key in the [custom slot mapping](https://rasa.com/docs/rasa/next/domain#custom-slot-mappings),
since the default action [`action_extract_slots`](https://rasa.com/docs/rasa/next/default-actions#action_extract_slots) runs `action_validate_slot_mappings`
automatically if present in the `actions` section of the domain.
