Often when it's mentioned it's treated as a hard rule, claiming semver has no justification as any change is a breaking change.
Though in practice most software packages are not used extensively to the point that any observable behavior is depended upon (and Hyrum himself opens with this caveat "With a sufficient number of users ...").
Though in practice most software packages are not used extensively to the point that any observable behavior is depended upon (and Hyrum himself opens with this caveat "With a sufficient number of users ...").