It’s actually valid semver during 0.x.x releases. https://semver.org/#spec-item-4
Technically according to spec you can do anything during 0.x.x releases but it’s common convention to push the meanings across one place so:
- 0.5.3 > 0.6.0 = major bump
- 0.5.3 > 0.5.4 = minor bump
- No way to define a patch bump
This is the convention we’ve been following since initial launch of 0.1.0.