#2677: add note that not all functions may accept keyword args.
diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst
index 299ff56..c148533 100644
--- a/Doc/reference/expressions.rst
+++ b/Doc/reference/expressions.rst
@@ -663,6 +663,14 @@
raised. Otherwise, the list of filled slots is used as the argument list for
the call.
+.. note::
+
+ An implementation may provide builtin functions whose positional parameters do
+ not have names, even if they are 'named' for the purpose of documentation, and
+ which therefore cannot be supplied by keyword. In CPython, this is the case for
+ functions implemented in C that use :cfunc:`PyArg_ParseTuple` to parse their
+ arguments.
+
If there are more positional arguments than there are formal parameter slots, a
:exc:`TypeError` exception is raised, unless a formal parameter using the syntax
``*identifier`` is present; in this case, that formal parameter receives a tuple