Summary.OBSERVABLE_USERThe implementation side of observation. This should be held internally with the creator of the state. Only the OBSERVABLE signature should be exposed.
include OBSERVABLERegister a new value and get the token used to enable and disable it.
val activate : token -> unitActivate/deactive the value attached to the token.
val deactivate : token -> unitval is_active : token -> boolDetermine if the value for the given token is active.
val all_active : unit -> (string * value) listGet all of the active values