Added callback support

src/components/jsonviewer/Readme.md

@@ -224,7 +224,13 @@ editable_hook = (HookBuilder()
 ```
 
 ### `when_custom(condition)`
-Use custom condition objects for complex logic.
+Use custom condition objects or callable predicates for complex logic.
+
+The `when_custom()` method accepts either:
+- **Condition instances**: Objects that inherit from the `Condition` base class
+- **Callable predicates**: Functions that take a `HookContext` parameter and return a boolean
+
+When a callable is provided, it's automatically wrapped in a `PredicateCondition` class internally.
 
 ```python
 class BusinessLogicCondition(Condition):