Minor Description
Not every exception warrants a message from the user. Sometimes just goign to another page without a message is good enough. For instance, if a user needs to respond to a confirmation email to complete an account signup, the action may throw an exception is the account is already completed. In this case, it would be great to simply use <exception> to send them to the login page, but I cannot do this declaratively because @key is required. I say this should be optional.