#16057: Clarify why the base method default is called in custom encoders.

Original patch by Kushal Das.
diff --git a/Lib/json/encoder.py b/Lib/json/encoder.py
index e1ed21f..1d8b20c 100644
--- a/Lib/json/encoder.py
+++ b/Lib/json/encoder.py
@@ -166,6 +166,7 @@
                     pass
                 else:
                     return list(iterable)
+                # Let the base class default method raise the TypeError
                 return JSONEncoder.default(self, o)
 
         """