Update docs, op_registration.

docs/guides/plugins.md

@@ -57,7 +57,12 @@ Let's review the changes we made.
 
 The [`@op`](../reference/lynxkite-core/ops.md#lynxkite.core.ops.op) decorator registers a
 function as a LynxKite operation. The first argument is the name of the environment,
-the second argument is the name of the operation.
+the last argument is the name of the operation. Between the two, you can list the hierarchy of
+categories the operation belongs to. For example:
+
+```python
+@op("LynxKite Graph Analytics", "Machine learning", "Preprocessing", "Split train/test set")
+```
 
 When defining multiple operations, you can use
 [`ops.op_registration`](../reference/lynxkite-core/ops.md#lynxkite.core.ops.op_registration)

lynxkite-core/src/lynxkite/core/ops.py

@@ -417,14 +417,14 @@ def register_executor(env: str):
     return decorator
 
 
-def op_registration(env: str):
+def op_registration(env: str, *categories: str):
     """Returns a decorator that can be used for registering functions as operations."""
-    return functools.partial(op, env)
+    return functools.partial(op, env, *categories)
 
 
-def passive_op_registration(env: str):
+def passive_op_registration(env: str, *categories: str):
     """Returns a function that can be used to register operations without associated code."""
-    return functools.partial(register_passive_op, env)
+    return functools.partial(register_passive_op, env, *categories)
 
 
 def make_async(func):