DDSXTY14 — Data Representation for RTPS's Serialized Key

RTPS 2.3 section 9.4.5.3.1
"D=0 and K=1 means that the serializedPayload SubmessageElement contains the serialized Key."

XTypes section 7.4 "Data Representation" should define the rules for encoding an object of a type defined by the 7.2 "Type System" to a Key-only serialization.

Using what's currently in the spec, there are two potential interpretations:

a. follow all the encoding rules as for a full object (adding DHeader, EMHeader, etc.) but any part of that object that's not a key gets skipped, using 7.2.2.4.7 to determine what's a key

b. use the rules in 7.6.8 (which are explicitly only for a KeyHash) to get a KeyHolder object and then encode that

Specify how to so the serialization of the 'key fields' of a keyed type

Update 7.6.8 "Interoperability of Keyed Topics" to talk about this case.