In OpenLayers 4 changelogs, it explains:
Unlike the switch from v2.x to v3.x, which marked a complete rewrite of the library with an entirely new API, major version increments now simply mean that users should pay attention to the 'Breaking changes' section of the upgrade notes.
But "semanting versioning" says:
MAJOR version increases when you make incompatible API changes
So, I don't understand: if the OL API is not changed, why OL major version did it increase to 4 ? Can someone explain better?