Updated 4.1 and 4.3 based on Jinmei's comments.

- Section 4.1: this is not necessarily accurate, since NoBinding is
  used for all current IAs (and could also be used for future ones as
  its concept is quite generic):

   While a Status Code option is implicitly bound to a specific type of
   IA,

- Section 4.1: s/addresses/some stateful option types/ so the
  description is generic?

   With the introduction of multiple IA option
   types, there might be a case where a server is not willing to offer
   addresses, but might be willing to offer other stateful option types.

  BTW, I wonder whether "resources" may be better than "stateful
  option (types)" in this context (see above).

- Section 4.1: this sentence should probably be generalized:

   Clients MUST be prepared to handle each of the following Advertise
   messages formats when there are no addresses available (even when no
   IA_PD was in the Solicit):

  e.g. by avoiding to use "addresses" or "IA_PD".

- Section 4.2: this text should probably be generalized (not
  hardcoding "address" etc)

   With (this includes the changes made by [RFC7083]):

     The client MUST ignore any Advertise message that contains no
     addresses (IAADDR options encapsulated in IA_NA or IA_TA options)
     [...]

- Section 4.3: regarding this behavior:

   Proposed solution: [...]  To deal
   with the case where servers have not yet been updated to do that,
   clients MUST use the shortest (explicit or implicit) T1/T2 timer
   (larger than 0) in any IA options in the Reply.  Longer T1/T2 timers
   are ignored.

  what should happen if we have two sets of T1/T2?
  - T1a = 10, T2a = 20
  - T1b = 0, T2b = 5
  If we pick up the shortests (> 0), T1 would be 10 and T2 would be
  5, which is an invalid combination.