Grabbed dndbeyond's source code

```
~/go/bin/sourcemapper -output ddb -jsurl https://media.dndbeyond.com/character-app/static/js/main.90aa78c5.js
```

ddb_main/packages/rules-engine/es/engine/OptionalClassFeature/derivers.js

@@ -0,0 +1,9 @@
+import { DefinitionHacks, DefinitionTypeEnum } from '../Definition';
+/**
+ * use hack until ids are strings
+ *
+ * @param id
+ */
+export function deriveDefinitionKey(id) {
+    return DefinitionHacks.hack__generateDefinitionKey(DefinitionTypeEnum.CLASS_FEATURE, id);
+}