With v257 we added three new fields to it: RELEASE_TYPE= encodes what kind of OS release the system is on – it takes "stable", "lts", "development" or "experiment" as value. In particular the latter is useful to use as hint for modifying the system's UI slightly to indicate that the system is running an experimental OS release.

The two other new fields EXPERIMENT= and EXPERIMENT_URL= may be used include additional metainformation about the release if it is marked as "experiment".