- Validation Interceptor does the actual validation. It calls the validate() method of the action. If there are any @validation annotation or if there are any xml files (ActionClass-validation.xml) it checks these validations. It also adds error messages if there are any during validation.
- WorkFlow Interceptor which checks for these errors, and changes the flow based on the result of the error. You can change the default behavior of the workflow by implementing ValidationWorkflowAware or using @InputConfig annotation.
The workflow documentation is not so update, I suggest you take a look at the source of DefaultWorkflowInterceptor which is very easy to understand.