I reviewed draft-ietf-core-problem-details on behalf of the  ops directorate. I nsummar y this draft is largely ready. I have one perhaps clarifying question.

in the regards to the following statement:

   Consumers of a Concise Problem Details data item MUST ignore any
   Custom Problem Detail entries, or keys inside the Custom Problem
   Detail entries, that they do not recognize; this allows Custom
   Problem Detail entries to evolve and include additional information
   in the future.  The assumption is that this is done in a backward and
   forward compatible way.

This seems like less of a gesture at compatibility as opposed to simply ignoring conditions that would otherwise produce errors by the receiving parties. it would see likely that coap problem detail collectors may collect such data for processing by other systems since the whole collection pipline may not move in lock step or doesn't it?