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.