DDSXTY14 — Extensibility of inherited structures

The specification should state the behavior if a derived type extensibility kind is specified to be different from that of its parent.

Furthermore for usability we should specify the behavior if the derived type does not specify any extensibility kind. Does it 'inherit' that of the parent or is it assumed to be the 'default'.

Current thinking: It is an error to have a derived structure specify a different extensibility kind than its parent. Leaving it unspecified sets the derived type extensibility type to that of your parent.

Basically the serialization of the derived class does not add its own header.