At present, the web application determines where to redirect to after saving a form.
Sometimes a particular form wants to be able to determine the page you are redirected to dynamically, e.g. based on details in the form, or the patient's current status.
(Example from Mirebalais: if you enter a Note with disposition = Death, and the patient doesn't have a death certificate, you should be redirected to the death certificate page. Otherwise, follow the standard UI flow.)
FormEntrySession should allow you to set the page to go to after successful form submission, and this should be settable by form submission actions.
Ideally, we'd have a tag that supports several ways of specifying things: