[NNTP] Terminology valid/invalid in RFC 3977

Following a discussion with Alfred H=F6nes, who reported:

> terminological overloading,
>     leading to ambiguity and under-specification
>
> Within the RFC text, the terms "valid", and in particular, "invalid",
> are used with three very distinct semantics.
> These terms could mean:
>
> a)
> conformance/non-conformance with the prescribed syntax (ABNF) for
> a message (command/reply), or one of its components, e.g., talking
> about a "valid response code" (Section 5.1.1 et al.)

I believe this one is pretty clear and without any ambiguity.

Let's deal with the other uses below.




> b)
> the special value "invalid" introduced in Section 6.1, on page 36,
> for the two NNTP session state variables specified:
>
>   The following commands are used to set the "currently selected
>   newsgroup" and the "current article number", which are used by
>   various commands.  At the start of an NNTP session, both of these
>   values are set to the special value "invalid".
>                                       ^^^^^^^^^

I think it is OK.




> c)
> the semantical validity of a newsgroup name or an article number
> (i.e., the 'existence' of a named group or article on the server);
> e.g. (second paragraph of Section 6.1.1.2, on page 36):
>
>   The required argument is the name of the newsgroup to be selected
>   (e.g., "news.software.nntp").  A list of valid newsgroups may be
>                                            ^^^^^
>   obtained by using the LIST ACTIVE command (see Section 7.6.3).
[...]
> The resulting ambiguity can perhaps most strikingly be seen from the
> second paragraph on page 38 (within the GROUP command Description,
> Section 6.1.1.2):
>
>           vvvvv
> |  When a valid group is selected by means of this command, the
>   currently selected newsgroup MUST be set to that group, and the
>   current article number MUST be set to the first article in the group
>   (this applies even if the group is already the currently selected
>   newsgroup).  If an empty newsgroup is selected, the current article
> |  number is made invalid.  If an invalid group is specified, the
>           !!!!!!!!!!!!!!!         ^^^^^^^
>   currently selected newsgroup and current article number MUST NOT be
>   changed.

Maybe it should be explained.  I do not know what is the best
thing to do here.  It is true that "valid" here means it is selectable
by a GROUP/LISTGROUP command and will lead to a valid currently
selected newsgroup.

(A suggestion was to use "undefined" instead of "invalid". Or to use
typographical enhancement to spell it:  `invalid' with surrounding
single back-quotes.)



> This also includes the situation where (at least) one of the above
> two state variables becomes 'lame' -- that is perhaps described best,
> for the latter variable, by the text on mid-page 47,
>               vvvvvvvvvvvvvvvv                           vvvvvvv
>  "Note that a previously valid article number MAY become invalid if the
>   article has been removed.  A previously invalid article number MAY
>   vvvvvvvvvvvv               ^^^^^^^^^^^^^^^^^^^^
>   become valid if the article has been reinstated, but this article
>   number MUST be no less than the reported low water mark for that
>   group."

You're right.  That is a very unfortunate use of "valid"/"invalid".
Taken into account in erratum 2037:

    http://www.rfc-editor.org/errata_search.php?eid=3D2037

New wording used:

   Note that a previously valid article number MAY cease to refer to any
   article if that article has been removed, in which case use of that
   article number (explicitly or implicitly) will cause a 423 response.  =
A
   previously removed article may be reinstated (but its number MUST be n=
o
   less than the reported low water mark for that group), in which case
   that number will once again refer to that article.




To the working group:  do you think something should be changed
regarding the problem c) mentioned in this mail?

--=20
Julien =C9LIE

=AB La science consiste =E0 passer d'un =E9tonnement =E0 l'autre. =BB
  (Aristote)