Issue #10285: explain the `flag` return field better in NNTP.list().

Patch by Julien Élie.

Doc/library/nntplib.rst

@@ -188,8 +188,17 @@ response indicates an error, the method raises one of the above exceptions.
    list of tuples representing all the groups available from this NNTP server.
    Each tuple has the form ``(group, last, first, flag)``, where
    *group* is a group name, *last* and *first* are the last and first article
-   numbers, and *flag* is ``'y'`` if posting is allowed, ``'n'`` if not,
-   and ``'m'`` if the newsgroup is moderated.  (Note the ordering: *last*, *first*.)
+   numbers, and *flag* usually takes one of these values:
+
+   * ``y``: Local postings and articles from peers are allowed.
+   * ``m``: The group is moderated and all postings must be approved.
+   * ``n``: No local postings are allowed, only articles from peers.
+   * ``j``: Articles from peers are filed in the junk group instead.
+   * ``x``: No local postings, and articles from peers are ignored.
+   * ``=foo.bar``: Articles are filed in the ``foo.bar`` group instead.
+
+   If *flag* has another value, then the status of the newsgroup should be
+   considered unknown.
 
    This command will often return very large results.  It is best to cache the
    results offline unless you really need to refresh them.

Misc/ACKS

@@ -238,6 +238,7 @@ Grant Edwards
 John Ehresman
 Eric Eisner
 Andrew Eland
+Julien Élie
 Lance Ellinghaus
 David Ely
 Jeff Epler