What parts of a spec should be normative?

Hi editors,

I left a comment in https://github.com/w3c/vc-data-model/issues/1285 that a
particular section shouldn't be marked non-normative, and the editors there
disagree with me. Do we have a document somewhere that gives guidelines for
what should be normative vs not? In this case it's "just statements that
use RFC 2119 keywords" vs "and definitions those statements depend on", but
I'm sure there have been other disagreements like this.

Thanks,
Jeffrey