Almost all code is aspirational in terms of matching a spec, being backwards compatible, not having bugs, etc. Its meaningless to talk about what is guaranteed

Almost all code is aspirational in terms of matching a spec, being backwards compatible, not having bugs, etc. Its meaningless to talk about what is guaranteed with respect to practically every piece of software in existence. What is important to a developer is "what is the risk that upgrading this software will break my deployment, and what do I gain from upgrading it", which semver relays to the developer to the best of the library author's ability.