The feature request relates to the wgConditionalUserOptions feature. While built-in conditions in ConditionalDefaultsLookup are for general purpose usage: CUDCOND_AFTER, CUDCOND_ANON, CUDCOND_NAMED, there are case where it would be useful to evaluate a more specific condition which does not fit or belong to MW core. An example of use cases is T376266 where the goal is to bucket users but the bucketing logic is opinionated and designed for Growth team experiments needs rather than a generic bucketing system.

For such cases it would be convenient to be able to "register" a new condition so ConditionalDefaultsLookup takes it into account when returning a user option.

Acceptance criteria

• Extensions can register their own conditions for CUD to evaluate