885 B
Public API thoughts
Possible "public API" candidates for semantic versioning/defining backward compatibility.
File format
On the face of it, an ideal candidate. However, it is actually very unlikely to be changed by us (since timeclock.el is the upstream), so semantic versioning based entirely on this might just leave us stuck on v1 forever. (Which might be a good thing, too.)
May be extended in the distant future (i.e. support for another format).
We did change it, abandoning timeclock.el as a backend. I'm mulling over an SQL backend. Will warrant a major version bump, if it means deprecating the s-expression backend.
Custom variables
Are definitely meant for the user.
Change in name or removal = major version bump.
Commands (user-facing functions)
May change in behaviour often, but changes in name or removal can justify a major version bump.