if (Client::isCoreFeatureEnabled(Quassel::Feature::FeatureName)) { ... }
```
+Depending on the type of protocol change, you might also need to update
+[`serializers.cpp`][file-cpp-serializers] and related files.
+
8. **Test everything! Upgrade, migrate, new setups, new client/old core,
old client/new core, etc.**
[file-cpp-sqlite]: ../sqlitestorage.cpp
[file-sh-upgradeschema]: upgradeSchema.sh
[file-h-quassel]: ../../common/quassel.h
+[file-cpp-serializers]: ../../common/serializers/serializers.cpp