bpo-38096: Complete the "structseq" and "named tuple" cleanup (GH-16010)

Doc/glossary.rst

@@ -757,7 +757,7 @@ Glossary
       Some named tuples are built-in types (such as the above examples).
       Alternatively, a named tuple can be created from a regular class
       definition that inherits from :class:`tuple` and that defines named
-      fields.  Such as class can be written by hand or it can be created with
+      fields.  Such a class can be written by hand or it can be created with
       the factory function :func:`collections.namedtuple`.  The latter
       technique also adds some extra methods that may not be found in
       hand-written or built-in named tuples.

Objects/structseq.c

@@ -1,5 +1,11 @@
-/* Implementation helper: a struct that looks like a tuple.  See timemodule
-   and posixmodule for example uses. */
+/* Implementation helper: a struct that looks like a tuple.
+   See timemodule and posixmodule for example uses.
+
+   The structseq helper is considered an internal CPython implementation
+   detail.  Docs for modules using structseqs should call them
+   "named tuples" (be sure to include a space between the two
+   words and add a link back to the term in Docs/glossary.rst).
+*/
 
 #include "Python.h"
 #include "pycore_tupleobject.h"