Comments
A profile extending another profile/resource must define a parent base and a differential section that defines the extension (optionally with the snapshot element). This makes sense.

However, the differential for core resource profiles (e.g. Immunization, Procedure, etc.) is entirely duplicating the snapshot element. This is mostly an artifact of the profile generation and publishing tools rather than the FHIR spec but the spec (e.g. profile section 6.17) should clearly differentiate between top-level profiles (those with no base) and those with a base.

Disposition WG
FHIR Core Team

Grahame's Comments
need to consider this. I think there's a better solution, to split out definitions and profiles. Relationship between Extensiondefinition, DataElement and Profile needs to be reconsidered