Placeholder editions for testing feature resolution. These should not be used or relied on outside of tests.

Editions that have been released. The specific values are arbitrary and should not be depended on, but they will always be time-ordered for easy comparison.

A placeholder edition for specifying default behaviors *before* a feature was first introduced. This is effectively an "infinite past".

Placeholder for specifying unbounded edition support. This should only ever be used by plugins that can expect to never require any changes to support a new edition.

Legacy syntax "editions". These pre-date editions, but behave much like distinct editions. These can't be used to specify the edition of proto files, but feature definitions must supply proto2/proto3 defaults for backwards compatibility.

A placeholder for an unknown edition value.

A placeholder edition for developing and testing unscheduled features.