diff --git a/README.md b/README.md
index 7042ba1..e428eba 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # ditto: dependency injection tool
 
-ditto is a simple and lightweight dependency injection tool for Python, now with support for nullable arguments.
+ditto is a simple and lightweight dependency injection tool for Python, with support for nullable arguments and parent class registration.
 
 ## Features
 
@@ -8,6 +8,7 @@ ditto is a simple and lightweight dependency injection tool for Python, now with
 - Supports class and instance-based services
 - Sync and Async support
 - Nullable argument handling
+- Parent class registration
 
 ## Installation
 
@@ -72,9 +73,47 @@ def battle(charmander: FirePokemon):
 battle()  # 'Ember ! 🔥'
 ```
 
+## Advanced Usage
+
+### Type Lookup in Registry
+
+ditto uses the lowercase name of the class as the key in its registry:
+
+```python
+di.register(Charmander)
+
+# These will all retrieve the Charmander instance:
+fire_pokemon = di.ServiceRegistry.get_instance().get('firepokemon')
+charmander = di.ServiceRegistry.get_instance().get('charmander')
+```
+
+This is particularly useful to understand when working with optional dependencies or when overriding parent class implementations.
+
+### Asynchronous Support
+
+ditto supports dependency injection for asynchronous functions:
+
+```python
+import asyncio
+
+class AsyncPokemon:
+    async def attack(self) -> str:
+        await asyncio.sleep(1)
+        return "Async attack!"
+
+di.register(AsyncPokemon)
+
+@di.inject
+async def async_battle(pokemon: AsyncPokemon):
+    result = await pokemon.attack()
+    print(result)
+
+asyncio.run(async_battle())  # Output: Async attack!
+```
+
 ### Nullable Argument Handling
 
-ditto now supports nullable arguments, allowing you to specify optional dependencies:
+ditto supports nullable arguments, allowing you to specify optional dependencies:
 
 ```python
 from typing import Optional
@@ -98,6 +137,107 @@ In this example:
 - `charmander` is a required dependency and must be registered.
 - `optional_pokemon` is an optional dependency. If it's not registered, `None` will be injected.
 
+**Note on Type Registration for Optional Parameters:**
+For both `Pokemon` and `Optional[Pokemon]`, ditto uses the same key (`'pokemon'`) in its registry. The `Optional` wrapper doesn't affect the registration key; it only changes how ditto handles the case when the service isn't found.
+
+### Parent Class Registration
+
+When you register a service class, ditto automatically registers it under its immediate parent class as well:
+
+```python
+class Pokemon:
+    pass
+
+class FirePokemon(Pokemon):
+    pass
+
+class Charmander(FirePokemon):
+    pass
+
+di.register(Charmander)
+
+@di.inject
+def train(fire_pokemon: FirePokemon, charmander: Charmander):
+    print(f"Training: {fire_pokemon.__class__.__name__}, {charmander.__class__.__name__}")
+
+train()  # Output: Training: Charmander, Charmander
+
+@di.inject
+def catch(pokemon: Pokemon):
+    print(f"Trying to catch: {pokemon.__class__.__name__}")
+
+catch()  # This will raise a ValueError: Service 'pokemon' not found.
+```
+
+In this example:
+- Registering `Charmander` also makes it available when `FirePokemon` (its immediate parent class) is requested.
+- However, `Pokemon` (the grandparent class) is not automatically registered.
+- This allows for one level of inheritance in dependency injection.
+
+
+### Error Handling and Common Pitfalls
+
+1. Missing dependencies:
+   If a required dependency is not registered, ditto will raise a `ValueError`:
+
+   ```python
+   @di.inject
+   def use_unregistered(service: NotInPokedexPokemon):
+       pass
+
+   use_unregistered()  # Raises ValueError: Service 'notinpokedexpokemon' not found.
+   ```
+
+2. Circular dependencies:
+   ditto doesn't automatically resolve circular dependencies. Be cautious when designing your dependency graph.
+
+### Multiple Registrations
+
+When multiple classes are registered for the same type, ditto will use the most recently registered one:
+
+```python
+class Pikachu(Pokemon):
+    pass
+
+class Charmander(Pokemon):
+    pass
+
+di.register(Pikachu)
+di.register(Charmander)
+
+@di.inject
+def catch(pokemon: Pokemon):
+    print(f"Caught a {pokemon.__class__.__name__}")
+
+catch()  # Output: Caught a Charmander
+```
+
+### Best Practices
+
+1. Register dependencies at the application's entry point.
+2. Use interfaces (abstract base classes) for better decoupling.
+3. Avoid registering too many concrete implementations to keep your dependency graph simple.
+
+### Managing Registered Services
+
+To unregister a service:
+
+```python
+# Unregister a service
+ServiceRegistry.get_instance()._services.pop('pokemon', None)
+
+```
+
+## Limitations
+
+- ditto doesn't support automatic constructor injection. Parameters must be explicitly annotated.
+- Circular dependencies are not automatically resolved and may cause issues if not carefully managed.
+
+## Contributing
+
+Contributions are welcome! Please feel free to submit a Pull Request.
+
+
 ## License
 
 This project is licensed under the MIT License - see the LICENSE file for details.
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