datatype readiness a = Ready of a | Waiting | Invalid of string
datatype rpcResult a = Success of a | Failure of string

val warning : a ::: Type -> signal (readiness a) -> xbody

val warningFmt : a ::: Type -> ctx ::: {Unit} -> [ctx ~ body] 
    => (string -> xml (ctx ++ body) [] []) -> signal (readiness a) 
    -> xml (ctx ++ body) [] []
(* A version of warning that adds a chrome wrapper to the warning message. *)