1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +---------------+---------------+-------+-----------------------+
  |     Kind      |    Length     |Subtype|                       |
  +---------------+---------------+-------+                       |
  |                     Subtype-specific data                     |
  |                       (variable length)                       |
  +---------------------------------------------------------------+