However, the absence of atom:summary is not an error and software MUST NOT fail to function correctly as a consequence of such an absence."
We don't use the term 'software' in the draft. We discuss Atom Processors.
If we were to define Atom Processors in opposition to an 'application', as in PaceDefineAtomProcessor, we could say a lot about applications. Note that one major goal of PaceDefineAtomProcessor is to avoid making normative requirements on applications.