Document collapse operator

docs/source/reference/index.rst

@@ -8,5 +8,6 @@ components.
     :maxdepth: 2
 
     cli
-    operators
     recipe-format
+    operators
+    internal

docs/source/reference/internal.rst

@@ -0,0 +1,36 @@
+Internal Functions
+==================
+
+This page details various internal functions within CSET. Most people should
+never have to worry about these, but they are documented here for the
+convenience of those developing CSET.
+
+CSET.operators
+--------------
+
+.. automodule:: CSET.operators
+   :members:
+
+CSET.recipes
+------------
+
+.. automodule:: CSET.recipes
+   :members:
+
+CSET.graph
+----------
+
+.. automodule:: CSET.graph
+   :members:
+
+CSET._common
+------------
+
+.. note::
+
+    While no functions documented on this page are part of any API promise, the
+    functions inside _common are especially liable to change without any kind of
+    notice.
+
+.. automodule:: CSET._common
+   :members:

docs/source/reference/operators.rst

@@ -5,6 +5,12 @@ This page details the operators contained within CSET. It is automatically
 generated from the code and its docstrings. Operators should be used via
 :doc:`/usage/operator-recipes`.
 
+CSET.operators.collapse
+-----------------------
+
+.. automodule:: CSET.operators.collapse
+   :members:
+
 CSET.operators.constraints
 --------------------------
 

src/CSET/operators/misc.py

@@ -27,11 +27,10 @@ def noop(x, **kwargs):
     x: Any
         Input to return.
 
-    Will silently accept any additional keyword arguments for testing purposes.
-
     Returns
     -------
     x: Any
         The input that was given.
     """
+
     return x