cabal-version semantics

[ulysses4ever]

What is wrong with the docs?
I don't see a place where the semantics of cabal-version is documented. It could go to CONTRIBUTING.md (as a start?) because Cabal devs contribute features that prompt version bumps. Another place is the log for the version updates in the manual:

• https://cabal.readthedocs.io/en/3.10/file-format-changelog.html

Additional context
We have been getting requests to clarify the policy around cabal-version more often lately. E.g.

• Fix #9534 Add constructor PPC64LE to type Arch, for powerpc64le #9535 (comment)

One place that looks relevant is https://github.com/haskell/cabal/wiki/Package-Description-Semantics but it looks completely in the woods and ancient.

A recent and very relevant discussion:

• PackageInfo functionality is not guarded behind cabal-version. #9331