diff --git a/examples/atari/atari_wrapper.py b/examples/atari/atari_wrapper.py
index e8023b7..2f098b3 100644
--- a/examples/atari/atari_wrapper.py
+++ b/examples/atari/atari_wrapper.py
@@ -383,6 +383,11 @@ class AtariEnvFactory(EnvFactoryRegistered):
         )
 
     class EnvPoolFactory(EnvPoolFactory):
+        """Atari-specific envpool creation.
+        Since envpool internally handles the functions that are implemented through the wrappers in `wrap_deepmind`,
+        it sets the creation keyword arguments accordingly.
+        """
+
         def __init__(self, parent: "AtariEnvFactory"):
             self.parent = parent
             if self.parent.scale:
@@ -393,6 +398,7 @@ class AtariEnvFactory(EnvFactoryRegistered):
 
         def _transform_task(self, task: str) -> str:
             task = super()._transform_task(task)
+            # TODO: Maybe warn user, explain why this is needed
             return task.replace("NoFrameskip-v4", "-v5")
 
         def _transform_kwargs(self, kwargs: dict, mode: EnvMode) -> dict:
diff --git a/tianshou/highlevel/env.py b/tianshou/highlevel/env.py
index 0c07035..5327794 100644
--- a/tianshou/highlevel/env.py
+++ b/tianshou/highlevel/env.py
@@ -270,7 +270,9 @@ class DiscreteEnvironments(Environments):
 
 
 class EnvPoolFactory:
-    """A factory for the creation of envpool-based vectorized environments."""
+    """A factory for the creation of envpool-based vectorized environments, which can be used in conjunction
+    with :class:`EnvFactoryRegistered`.
+    """
 
     def _transform_task(self, task: str) -> str:
         return task
@@ -294,7 +296,7 @@ class EnvPoolFactory:
         mode: EnvMode,
         seed: int,
         kwargs: dict,
-    ) -> BaseVectorEnv | None:
+    ) -> BaseVectorEnv:
         import envpool
 
         envpool_task = self._transform_task(task)
@@ -308,6 +310,8 @@ class EnvPoolFactory:
 
 
 class EnvFactory(ToStringMixin, ABC):
+    """Main interface for the creation of environments (in various forms)."""
+
     def __init__(self, venv_type: VectorEnvType):
         """:param venv_type: the type of vectorized environment to use"""
         self.venv_type = venv_type
@@ -346,7 +350,8 @@ class EnvFactory(ToStringMixin, ABC):
 
 class EnvFactoryRegistered(EnvFactory):
     """Factory for environments that are registered with gymnasium and thus can be created via `gymnasium.make`
-    (or via `envpool.make_gymnasium`)."""
+    (or via `envpool.make_gymnasium`).
+    """
 
     def __init__(
         self,