OK - I've added this. The resulting paragraph looks like:

<modified text>

4.6.38.  Vendor Specific Payload

   The Vendor Specific Payload message element is used to communicate
   vendor specific information between the WTP and the AC.  The Vendor
   Specific Payload message element MAY be present in any CAPWAP
   message.  The exchange of vendor specific data between the MUST NOT
   modify the behavior of the base CAPWAP protocol and state machine.
   The message element uses the following format:
</modified text>

> Section 4.6.38., paragraph 0:
> > 4.6.38.  Vendor Specific Payload
> 
>   I'd add a statement in this section along the lines of: "The
exchange
>   of vendor specific data between the MUST NOT modify the behavior of
>   the base CAPWAP protocol and state machine." Otherwise we're
creating
>   a hole for incompatibilities.

OK - I've added this.