Raised when a spec module violates one of the rules in 02-dsl-semantics.md.

Every rule in that document is enforced when the spec module compiles, so a spec either means something precise or does not compile. The message quality is a deliverable rather than a nicety (02-dsl-semantics.md §7): a diagnostic carries the spec module, the declaration it came from, the offending line, and — where there is one — the form the author probably meant to write.

kind — the name the diagnostic is known by

Every diagnostic carries a kind, a stable identifier: the first column of the diagnostics table in 02-dsl-semantics.md §7 is the kind. It is required, so a diagnostic without one cannot be raised, and the set of kinds stays closed.