Based on the design discussion for the KVCatalog versioning scheme, the feature document in SERVER-23116 has separate fields for "repairable" and "non-repairable" feature bits. The distinction between the "repairable" and "non-repairable" feature bits is that the "repairable" features are no longer in use after dropping and re-creating the indexes on the collection with an older version of MongoDB. A user would then be able to downgrade to an older version of MongoDB that didn't recognize the new feature by first running --repair.