(1)
  +-------+-------+-------+---------+
  | Block | Data  | Block | Clear   |
  | Gap   | Block | Gap   | Trailer |
  +-------+-------+-------+---------+

Or:

(2)
  +-------+-------+-------+-------+---------+
  | Block | Data  | Block | Data  | Clear   |
  | Gap   | Block | Gap   | Block | Trailer |
  +-------+-------+-------+-------+---------+
                               ^
                               |
                           (Partially
                            Written)