(named list) Specifies from what sources the Shiny progress
elements 'message' and 'detail' should be updated. Valid sources are
"message", "sticky_message" and "non_sticky_message", where
"message" is short for c("non_sticky_message", "sticky_message"). For
example, inputs = list(message = "sticky-message", detail = "message")
will update the Shiny 'message' component from sticky messages only,
whereas the 'detail' component is updated using any message.