Document the expected convention for getstate() (as explained to me by Guido).
diff --git a/Lib/codecs.py b/Lib/codecs.py
index 06cec17..6d8d554 100644
--- a/Lib/codecs.py
+++ b/Lib/codecs.py
@@ -259,7 +259,9 @@
def getstate(self):
"""
Return the current state of the decoder. This must be a
- (buffered_input, additional_state_info) tuple.
+ (buffered_input, additional_state_info) tuple. By convention,
+ additional_state_info should represent the state of the decoder
+ WITHOUT yet having processed the contents of buffered_input.
"""
return (b"", 0)