[DFDL-WG] Optional Initiator and Terminator?

Is there a way to specify that an initiator/terminator pair is optional? IOW, these are both valid: { data } data If not, which of these workarounds is better (and why)? Choice DataWithInitiatorAndTeminator DataWithoutInitiatorAndTeminator Or Sequence OptionalInitiator (0 to 1) Data OptionalTerminator (0 to 1) These seem the same to me, but maybe there's a reason why one is better.