This is Info file ../info/gnus.info, produced by Makeinfo-1.63 from the
input file gnus.texi.

   This file documents Gnus, the GNU Emacs newsreader.

   Copyright (C) 1995,96 Free Software Foundation, Inc.

   Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

   Permission is granted to copy and distribute modified versions of
this manual under the conditions for verbatim copying, provided also
that the entire resulting derived work is distributed under the terms
of a permission notice identical to this one.

   Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions.


File: gnus.info,  Node: Terminology,  Next: Customization,  Prev: History,  Up: Appendices

Terminology
===========

"news"
     This is what you are supposed to use this thing for--reading news.
     News is generally fetched from a nearby NNTP server, and is
     generally publicly available to everybody.  If you post news, the
     entire world is likely to read just what you have written, and
     they'll all snigger mischievously.  Behind your back.

"mail"
     Everything that's delivered to you personally is mail.  Some
     news/mail readers (like Gnus) blur the distinction between mail
     and news, but there is a difference.  Mail is private.  News is
     public.  Mailing is not posting, and replying is not following up.

"reply"
     Send a mail to the person who has written what you are reading.

"follow up"
     Post an article to the current newsgroup responding to the article
     you are reading.

"backend"
     Gnus gets fed articles from a number of backends, both news and
     mail backends.  Gnus does not handle the underlying media, so to
     speak--this is all done by the backends.

"native"
     Gnus will always use one method (and backend) as the "native", or
     default, way of getting news.

"foreign"
     You can also have any number of foreign groups active at the same
     time.  These are groups that use different backends for getting
     news.

"secondary"
     Secondary backends are somewhere half-way between being native and
     being foreign, but they mostly act like they are native.

"article"
     A nessage that has been posted as news.

"mail message"
     A message that has been mailed.

"message"
     A mail message or news article

"head"
     The top part of a message, where administrative information (etc.)
     is put.

"body"
     The rest of an article.  Everything that is not in the head is in
     the body.

"header"
     A line from the head of an article.

"headers"
     A collection of such lines, or a collection of heads.  Or even a
     collection of NOV lines.

"NOV"
     When Gnus enters a group, it asks the backend for the headers of
     all unread articles in the group.  Most servers support the News
     OverView format, which is more compact and much faster to read and
     parse than the normal HEAD format.

"level"
     Each group is subscribed at some "level" or other (1-9).  The ones
     that have a lower level are "more" subscribed than the groups with
     a higher level.  In fact, groups on levels 1-5 are considered
     "subscribed"; 6-7 are "unsubscribed"; 8 are "zombies"; and 9 are
     "killed".  Commands for listing groups and scanning for new
     articles will all use the numeric prefix as "working level".

"killed groups"
     No information on killed groups is stored or updated, which makes
     killed groups much easier to handle than subscribed groups.

"zombie groups"
     Just like killed groups, only slightly less dead.

"active file"
     The news server has to keep track of what articles it carries, and
     what groups exist.  All this information in stored in the active
     file, which is rather large, as you might surmise.

"bogus groups"
     A group that exists in the `.newsrc' file, but isn't known to the
     server (i. e.,  it isn't in the active file), is a *bogus group*.
     This means that the group probably doesn't exist (any more).

"server"
     A machine than one can connect to and get news (or mail) from.

"select method"
     A structure that specifies the backend, the server and the virtual
     server parameters.

"virtual server"
     A named select method.  Since a select methods defines all there
     is to know about connecting to a (physical) server, taking the who
     things as a whole is a virtual server.


File: gnus.info,  Node: Customization,  Next: Troubleshooting,  Prev: Terminology,  Up: Appendices

Customization
=============

   All variables are properly documented elsewhere in this manual.  This
section is designed to give general pointers on how to customize Gnus
for some quite common situations.

* Menu:

* Slow/Expensive Connection:: You run a local Emacs and get the news elsewhere.
* Slow Terminal Connection::  You run a remote Emacs.
* Little Disk Space::         You feel that having large setup files is icky.
* Slow Machine::              You feel like buying a faster machine.


File: gnus.info,  Node: Slow/Expensive Connection,  Next: Slow Terminal Connection,  Up: Customization

Slow/Expensive NNTP Connection
------------------------------

   If you run Emacs on a machine locally, and get your news from a
machine over some very thin strings, you want to cut down on the amount
of data Gnus has to get from the NNTP server.

`gnus-read-active-file'
     Set this to `nil', which will inhibit Gnus from requesting the
     entire active file from the server.  This file is often v.  large.
     You also have to set `gnus-check-new-news' and
     `gnus-check-bogus-newsgroups' to `nil' to make sure that Gnus
     doesn't suddenly decide to fetch the active file anyway.

`gnus-nov-is-evil'
     This one has to be `nil'.  If not, grabbing article headers from
     the NNTP server will not be very fast.  Not all NNTP servers
     support XOVER; Gnus will detect this by itself.


File: gnus.info,  Node: Slow Terminal Connection,  Next: Little Disk Space,  Prev: Slow/Expensive Connection,  Up: Customization

Slow Terminal Connection
------------------------

   Let's say you use your home computer for dialing up the system that
runs Emacs and Gnus.  If your modem is slow, you want to reduce the
amount of data that is sent over the wires as much as possible.

`gnus-auto-center-summary'
     Set this to `nil' to inhibit Gnus from re-centering the summary
     buffer all the time.  If it is `vertical', do only vertical
     re-centering.  If it is neither `nil' nor `vertical', do both
     horizontal and vertical recentering.

`gnus-visible-headers'
     Cut down on the headers that are included in the articles to the
     minimum.  You can, in fact, make do without them altogether--most
     of the useful data is in the summary buffer, anyway.  Set this
     variable to `^NEVVVVER' or `From:', or whatever you feel you need.

`gnus-article-display-hook'
     Set this hook to all the available hiding commands:
          (setq gnus-article-display-hook
                '(gnus-article-hide-headers gnus-article-hide-signature
                  gnus-article-hide-citation))

`gnus-use-full-window'
     By setting this to `nil', you can make all the windows smaller.
     While this doesn't really cut down much generally, it means that
     you have to see smaller portions of articles before deciding that
     you didn't want to read them anyway.

`gnus-thread-hide-subtree'
     If this is non-`nil', all threads in the summary buffer will be
     hidden initially.

`gnus-updated-mode-lines'
     If this is `nil', Gnus will not put information in the buffer mode
     lines, which might save some time.


File: gnus.info,  Node: Little Disk Space,  Next: Slow Machine,  Prev: Slow Terminal Connection,  Up: Customization

Little Disk Space
-----------------

   The startup files can get rather large, so you may want to cut their
sizes a bit if you are running out of space.

`gnus-save-newsrc-file'
     If this is `nil', Gnus will never save `.newsrc'--it will only
     save `.newsrc.eld'.  This means that you will not be able to use
     any other newsreaders than Gnus.  This variable is `t' by default.

`gnus-save-killed-list'
     If this is `nil', Gnus will not save the list of dead groups.  You
     should also set `gnus-check-new-newsgroups' to `ask-server' and
     `gnus-check-bogus-newsgroups' to `nil' if you set this variable to
     `nil'.  This variable is `t' by default.


File: gnus.info,  Node: Slow Machine,  Prev: Little Disk Space,  Up: Customization

Slow Machine
------------

   If you have a slow machine, or are just really impatient, there are a
few things you can do to make Gnus run faster.

   Set`gnus-check-new-newsgroups' and `gnus-check-bogus-newsgroups' to
`nil' to make startup faster.

   Set `gnus-show-threads', `gnus-use-cross-reference' and
`gnus-nov-is-evil' to `nil' to make entering and exiting the summary
buffer faster.

   Set `gnus-article-display-hook' to `nil' to make article processing
a bit faster.


File: gnus.info,  Node: Troubleshooting,  Next: A Programmers Guide to Gnus,  Prev: Customization,  Up: Appendices

Troubleshooting
===============

   Gnus works *so* well straight out of the box--I can't imagine any
problems, really.

   Ahem.

  1. Make sure your computer is switched on.

  2. Make sure that you really load the current Gnus version.  If you
     have been running GNUS, you need to exit Emacs and start it up
     again before Gnus will work.

  3. Try doing an `M-x gnus-version'.  If you get something that looks
     like `Gnus v5.46; nntp 4.0' you have the right files loaded.  If,
     on the other hand, you get something like `NNTP 3.x' or `nntp
     flee', you have some old `.el' files lying around.  Delete these.

  4. Read the help group (`G h' in the group buffer) for a FAQ and a
     how-to.

   If all else fails, report the problem as a bug.

   If you find a bug in Gnus, you can report it with the `M-x gnus-bug'
command. `M-x set-variable RET debug-on-error RET t RET', and send me
the backtrace.  I will fix bugs, but I can only fix them if you send me
a precise description as to how to reproduce the bug.

   You really can never be too detailed in a bug report.  Always use the
`M-x gnus-bug' command when you make bug reports, even if it creates a
10Kb mail each time you use it, and even if you have sent me your
environment 500 times before.  I don't care.  I want the full info each
time.

   It is also important to remember that I have no memory whatsoever.
If you send a bug report, and I send you a reply, and then you send back
just "No, it's not! Moron!", I will have no idea what you are insulting
me about.  Always over-explain everything.  It's much easier for all of
us--if I don't have all the information I need, I will just mail you
and ask for more info, and everything takes more time.

   If the problem you're seeing is very visual, and you can't quite
explain it, copy the Emacs window to a file (with `xwd', for instance),
put it somewhere it can be reached, and include the URL of the picture
in the bug report.a

   If you just need help, you are better off asking on
`gnu.emacs.gnus'.  I'm not very helpful.

   You can also ask on the ding mailing list--`ding@ifi.uio.no'.  Write
to `ding-request@ifi.uio.no' to subscribe.


File: gnus.info,  Node: A Programmers Guide to Gnus,  Next: Emacs for Heathens,  Prev: Troubleshooting,  Up: Appendices

A Programmer's Guide to Gnus
============================

   It is my hope that other people will figure out smart stuff that Gnus
can do, and that other people will write those smart things as well.  To
facilitate that I thought it would be a good idea to describe the inner
workings of Gnus.  And some of the not-so-inner workings, while I'm at
it.

   You can never expect the internals of a program not to change, but I
will be defining (in some details) the interface between Gnus and its
backends (this is written in stone), the format of the score files
(ditto), data structures (some are less likely to change than others)
and general method of operations.

* Menu:

* Backend Interface::        How Gnus communicates with the servers.
* Score File Syntax::        A BNF definition of the score file standard.
* Headers::                  How Gnus stores headers internally.
* Ranges::                   A handy format for storing mucho numbers.
* Group Info::               The group info format.
* Emacs/XEmacs Code::        Gnus can be run under all modern Emacsen.
* Various File Formats::     Formats of files that Gnus use.


File: gnus.info,  Node: Backend Interface,  Next: Score File Syntax,  Up: A Programmers Guide to Gnus

Backend Interface
-----------------

   Gnus doesn't know anything about NNTP, spools, mail or virtual
groups.  It only knows how to talk to "virtual servers".  A virtual
server is a "backend" and some "backend variables".  As examples of the
first, we have `nntp', `nnspool' and `nnmbox'.  As examples of the
latter we have `nntp-port-number' and `nnmbox-directory'.

   When Gnus asks for information from a backend--say `nntp'--on
something, it will normally include a virtual server name in the
function parameters.  (If not, the backend should use the "current"
virtual server.)  For instance, `nntp-request-list' takes a virtual
server as its only (optional) parameter.  If this virtual server hasn't
been opened, the function should fail.

   Note that a virtual server name has no relation to some physical
server name.  Take this example:

     (nntp "odd-one"
           (nntp-address "ifi.uio.no")
           (nntp-port-number 4324))

   Here the virtual server name is `odd-one' while the name of the
physical server is `ifi.uio.no'.

   The backends should be able to switch between several virtual
servers.  The standard backends implement this by keeping an alist of
virtual server environments that it pulls down/pushes up when needed.

   There are two groups of interface functions: "required functions",
which must be present, and "optional functions", which Gnus will always
check whether are present before attempting to call.

   All these functions are expected to return data in the buffer
`nntp-server-buffer' (` *nntpd*'), which is somewhat unfortunately
named, but we'll have to live with it.  When I talk about "resulting
data", I always refer to the data in that buffer.  When I talk about
"return value", I talk about the function value returned by the
function call.

   Some backends could be said to be "server-forming" backends, and
some might be said to not be.  The latter are backends that generally
only operate on one group at a time, and have no concept of "server" -
they have a group, and they deliver info on that group and nothing more.

   In the examples and definitions I will refer to the imaginary backend
`nnchoke'.

* Menu:

* Required Backend Functions::        Functions that must be implemented.
* Optional Backend Functions::        Functions that need not be implemented.
* Writing New Backends::              Extending old backends.


File: gnus.info,  Node: Required Backend Functions,  Next: Optional Backend Functions,  Up: Backend Interface

Required Backend Functions
..........................

`(nnchoke-retrieve-headers ARTICLES &optional GROUP SERVER FETCH-OLD)'
     ARTICLES is either a range of article numbers or a list of
     `Message-ID's.  Current backends do not fully support either--only
     sequences (lists) of article numbers, and most backends do not
     support retrieval of `Message-ID's.  But they should try for both.

     The result data should either be HEADs or NOV lines, and the result
     value should either be `headers' or `nov' to reflect this.  This
     might later be expanded to `various', which will be a mixture of
     HEADs and NOV lines, but this is currently not supported by Gnus.

     If FETCH-OLD is non-`nil' it says to try to fetch "extra headers,
     in some meaning of the word.  This is generally done by fetching
     (at most) FETCH-OLD extra headers less than the smallest article
     number in `articles', and fill in the gaps as well.  The presence
     of this parameter can be ignored if the backend finds it
     cumbersome to follow the request.  If this is non-`nil' and not a
     number, do maximum fetches.

     Here's an example HEAD:

          221 1056 Article retrieved.
          Path: ifi.uio.no!sturles
          From: sturles@ifi.uio.no (Sturle Sunde)
          Newsgroups: ifi.discussion
          Subject: Re: Something very droll
          Date: 27 Oct 1994 14:02:57 +0100
          Organization: Dept. of Informatics, University of Oslo, Norway
          Lines: 26
          Message-ID: <38o8e1$a0o@holmenkollen.ifi.uio.no>
          References: <38jdmq$4qu@visbur.ifi.uio.no>
          NNTP-Posting-Host: holmenkollen.ifi.uio.no
          .

     So a `headers' return value would imply that there's a number of
     these in the data buffer.

     Here's a BNF definition of such a buffer:

          headers        = *head
          head           = error / valid-head
          error-message  = [ "4" / "5" ] 2number " " <error message> eol
          valid-head     = valid-message *header "." eol
          valid-message  = "221 " <number> " Article retrieved." eol
          header         = <text> eol

     If the return value is `nov', the data buffer should contain
     "network overview database" lines.  These are basically fields
     separated by tabs.

          nov-buffer = *nov-line
          nov-line   = 8*9 [ field <TAB> ] eol
          field      = <text except TAB>

     For a closer explanation what should be in those fields, *note
     Headers::..

`(nnchoke-open-server SERVER &optional DEFINITIONS)'
     SERVER is here the virtual server name.  DEFINITIONS is a list of
     `(VARIABLE VALUE)' pairs that defines this virtual server.

     If the server can't be opened, no error should be signaled.  The
     backend may then choose to refuse further attempts at connecting
     to this server.  In fact, it should do so.

     If the server is opened already, this function should return a
     non-`nil' value.  There should be no data returned.

`(nnchoke-close-server &optional SERVER)'
     Close connection to SERVER and free all resources connected to it.
     Return `nil' if the server couldn't be closed for some reason.

     There should be no data returned.

`(nnchoke-request-close)'
     Close connection to all servers and free all resources that the
     backend have reserved.  All buffers that have been created by that
     backend should be killed.  (Not the `nntp-server-buffer', though.)
     This function is generally only called when Gnus is shutting down.

     There should be no data returned.

`(nnchoke-server-opened &optional SERVER)'
     If SERVER is the current virtual server, and the connection to the
     physical server is alive, then this function should return a
     non-`nil' vlue.  This function should under no circumstances
     attempt to reconnect to a server that is has lost connection to.

     There should be no data returned.

`(nnchoke-status-message &optional SERVER)'
     This function should return the last error message from SERVER.

     There should be no data returned.

`(nnchoke-request-article ARTICLE &optional GROUP SERVER TO-BUFFER)'
     The result data from this function should be the article specified
     by ARTICLE.  This might either be a `Message-ID' or a number.  It
     is optional whether to implement retrieval by `Message-ID', but it
     would be nice if that were possible.

     If TO-BUFFER is non-`nil', the result data should be returned in
     this buffer instead of the normal data buffer.  This is to make it
     possible to avoid copying large amounts of data from one buffer to
     another, and Gnus mainly request articles to be inserted directly
     into its article buffer.

     If it is at all possible, this function should return a cons cell
     where the car is the group name the article was fetched from, and
     the cdr is the article number.  This will enable Gnus to find out
     what the real group and article numbers are when fetching articles
     by `Message-ID'.  If this isn't possible, `t' should be returned
     on successful article retrievement.

`(nnchoke-open-group GROUP &optional SERVER)'
     Make GROUP the current group.

     There should be no data returned by this function.

`(nnchoke-request-group GROUP &optional SERVER)'
     Get data on GROUP.  This function also has the side effect of
     making GROUP the current group.

     Here's an example of some result data and a definition of the same:

          211 56 1000 1059 ifi.discussion

     The first number is the status, which should be `211'.  Next is the
     total number of articles in the group, the lowest article number,
     the highest article number, and finally the group name.  Note that
     the total number of articles may be less than one might think
     while just considering the highest and lowest article numbers, but
     some articles may have been canceled.  Gnus just discards the
     total-number, so whether one should take the bother to generate it
     properly (if that is a problem) is left as an exercise to the
     reader.

          group-status = [ error / info ] eol
          error        = [ "4" / "5" ] 2<number> " " <Error message>
          info         = "211 " 3* [ <number> " " ] <string>

`(nnchoke-close-group GROUP &optional SERVER)'
     Close GROUP and free any resources connected to it.  This will be
     a no-op on most backends.

     There should be no data returned.

`(nnchoke-request-list &optional SERVER)'
     Return a list of all groups available on SERVER.  And that means
     *all*.

     Here's an example from a server that only carries two groups:

          ifi.test 0000002200 0000002000 y
          ifi.discussion 3324 3300 n

     On each line we have a group name, then the highest article number
     in that group, the lowest article number, and finally a flag.

          active-file = *active-line
          active-line = name " " <number> " " <number> " " flags eol
          name        = <string>
          flags       = "n" / "y" / "m" / "x" / "j" / "=" name

     The flag says whether the group is read-only (`n'), is moderated
     (`m'), is dead (`x'), is aliased to some other group
     (`=other-group' or none of the above (`y').

`(nnchoke-request-post &optional SERVER)'
     This function should post the current buffer.  It might return
     whether the posting was successful or not, but that's not
     required.  If, for instance, the posting is done asynchronously,
     it has generally not been completed by the time this function
     concludes.  In that case, this function should set up some kind of
     sentinel to beep the user loud and clear if the posting could not
     be completed.

     There should be no result data from this function.


File: gnus.info,  Node: Optional Backend Functions,  Next: Writing New Backends,  Prev: Required Backend Functions,  Up: Backend Interface

Optional Backend Functions
..........................

`(nnchoke-retrieve-groups GROUPS &optional SERVER)'
     GROUPS is a list of groups, and this function should request data
     on all those groups.  How it does it is of no concern to Gnus, but
     it should attempt to do this in a speedy fashion.

     The return value of this function can be either `active' or
     `group', which says what the format of the result data is.  The
     former is in the same format as the data from
     `nnchoke-request-list', while the latter is a buffer full of lines
     in the same format as `nnchoke-request-group' gives.

          group-buffer = *active-line / *group-status

`(nnchoke-request-update-info GROUP INFO &optional SERVER)'
     A Gnus group info (*note Group Info::.) is handed to the backend
     for alterations.  This comes in handy if the backend really
     carries all the information (as is the case with virtual an imap
     groups).  This function may alter the info in any manner it sees
     fit, and should return the (altered) group info.  This function
     may alter the group info destructively, so no copying is needed
     before boogeying.

     There should be no result data from this function.

`(nnchoke-request-type GROUP &optional ARTICLE)'
     When the user issues commands for "sending news" (`F' in the
     summary buffer, for instance), Gnus has to know whether the
     article the user is following up is news or mail.  This function
     should return `news' if ARTICLE in GROUP is news, `mail' if it is
     mail and `unknown' if the type can't be decided.  (The ARTICLE
     parameter is necessary in `nnvirtual' groups which might very well
     combine mail groups and news groups.)

     There should be no result data from this function.

`(nnchoke-request-update-mark GROUP ARTICLE MARK)'
     If the user tries to set a mark that the backend doesn't like, this
     function may change the mark.  Gnus will use whatever this function
     returns as the mark for ARTICLE instead of the original MARK.  If
     the backend doesn't care, it must return the original MARK, and
     not `nil' or any other type of garbage.

     The only use for this that I can see is what `nnvirtual' does with
     it--if a component group is auto-expirable, marking an article as
     read in the virtual group should result in the article being
     marked as expirable.

     There should be no result data from this function.

`(nnchoke-request-scan &optional GROUP SERVER)'
     This function may be called at any time (by Gnus or anything else)
     to request that the backend check for incoming articles, in one
     way or another.  A mail backend will typically read the spool file
     or query the POP server when this function is invoked.  The GROUP
     doesn't have to be heeded--if the backend decides that it is too
     much work just scanning for a single group, it may do a total scan
     of all groups.  It would be nice, however, to keep things local if
     that's practical.

     There should be no result data from this function.

`(nnchoke-request-asynchronous GROUP &optional SERVER ARTICLES)'
     This is a request to fetch articles asynchronously later.
     ARTICLES is an alist of (ARTICLE-NUMBER LINE-NUMBER).  One would
     generally expect that if one later fetches article number 4, for
     instance, some sort of asynchronous fetching of the articles after
     4 (which might be 5, 6, 7 or 11, 3, 909 depending on the order in
     that alist) would be fetched asynchronously, but that is left up
     to the backend.  Gnus doesn't care.

     There should be no result data from this function.

`(nnchoke-request-group-description GROUP &optional SERVER)'
     The result data from this function should be a description of
     GROUP.

          description-line = name <TAB> description eol
          name             = <string>
          description      = <text>

`(nnchoke-request-list-newsgroups &optional SERVER)'
     The result data from this function should be the description of all
     groups available on the server.

          description-buffer = *description-line

`(nnchoke-request-newgroups DATE &optional SERVER)'
     The result data from this function should be all groups that were
     created after `date', which is in normal human-readable date
     format.  The data should be in the active buffer format.

`(nnchoke-request-create-group GROUP &optional SERVER)'
     This function should create an empty group with name GROUP.

     There should be no return data.

`(nnchoke-request-expire-articles ARTICLES &optional GROUP SERVER FORCE)'
     This function should run the expiry process on all articles in the
     ARTICLES range (which is currently a simple list of article
     numbers.)  It is left up to the backend to decide how old articles
     should be before they are removed by this function.  If FORCE is
     non-`nil', all ARTICLES should be deleted, no matter how new they
     are.

     This function should return a list of articles that it did not/was
     not able to delete.

     There should be no result data returned.

`(nnchoke-request-move-article ARTICLE GROUP SERVER ACCEPT-FORM'
     &optional LAST)

     This function should move ARTICLE (which is a number) from GROUP
     by calling ACCEPT-FORM.

     This function should ready the article in question for moving by
     removing any header lines it has added to the article, and
     generally should "tidy up" the article.  Then it should `eval'
     ACCEPT-FORM in the buffer where the "tidy" article is.  This will
     do the actual copying.  If this `eval' returns a non-`nil' value,
     the article should be removed.

     If LAST is `nil', that means that there is a high likelihood that
     there will be more requests issued shortly, so that allows some
     optimizations.

     The function should return a cons where the car is the group name
     and the cdr is the article number that the article was entered as.

     There should be no data returned.

`(nnchoke-request-accept-article GROUP &optional SERVER LAST)'
     This function takes the current buffer and inserts it into GROUP.
     If LAST in `nil', that means that there will be more calls to this
     function in short order.

     The function should return a cons where the car is the group name
     and the cdr is the article number that the article was entered as.

     There should be no data returned.

`(nnchoke-request-replace-article ARTICLE GROUP BUFFER)'
     This function should remove ARTICLE (which is a number) from GROUP
     and insert BUFFER there instead.

     There should be no data returned.

`(nnchoke-request-delete-group GROUP FORCE &optional SERVER)'
     This function should delete GROUP.  If FORCE, it should really
     delete all the articles in the group, and then delete the group
     itself.  (If there is such a thing as "the group itself".)

     There should be no data returned.

`(nnchoke-request-rename-group GROUP NEW-NAME &optional SERVER)'
     This function should rename GROUP into NEW-NAME.  All articles
     that are in GROUP should move to NEW-NAME.

     There should be no data returned.


File: gnus.info,  Node: Writing New Backends,  Prev: Optional Backend Functions,  Up: Backend Interface

Writing New Backends
....................

   The various backends share many similarities.  `nnml' is just like
`nnspool', but it allows you to edit the articles on the server.
`nnmh' is just like `nnml', but it doesn't use an active file, and it
doesn't maintain overview databases.  `nndir' is just like `nnml', but
it has no concept of "groups", and it doesn't allow editing articles.

   It would make sense if it were possible to "inherit" functions from
backends when writing new backends.  And, indeed, you can do that if you
want to.  (You don't have to if you don't want to, of course.)

   All the backends declare their public variables and functions by
using a package called `nnoo'.

   To inherit functions from other backends (and allow other backends to
inherit functions from the current backend), you should use the
following macros: following.

`nnoo-declare'
     This macro declares the first parameter to be a child of the
     subsequent parameters.  For instance:

          (nnoo-declare nndir
            nnml nnmh)

     `nndir' has here declared that it intends to inherit functions from
     both `nnml' and `nnmh'.

`defvoo'
     This macro is equivalent to `defvar', but registers the variable as
     a public server variable.  Most state-oriented variables should be
     declared with `defvoo' instead of `defvar'.

     In addition to the normal `defvar' parameters, it takes a list of
     variables in the parent backends to map the variable to when
     executing a function in those backends.

          (defvoo nndir-directory nil
            "Where nndir will look for groups."
            nnml-current-directory nnmh-current-directory)

     This means that `nnml-current-directory' will be set to
     `nndir-directory' when an `nnml' function is called on behalf of
     `nndir'.  (The same with `nnmh'.)

`nnoo-define-basics'
     This macro defines some common functions that almost all backends
     should have.

          (nnoo-define-basics nndir)

`deffoo'
     This macro is just like `defun' and takes the same parameters.  In
     addition to doing the normal `defun' things, it registers the
     function as being public so that other backends can inherit it.

`nnoo-map-functions'
     This macro allows mapping of functions from the current backend to
     functions from the parent backends.

          (nnoo-map-functions nndir
            (nnml-retrieve-headers 0 nndir-current-group 0 0)
            (nnmh-request-article 0 nndir-current-group 0 0))

     This means that when `nndir-retrieve-headers' is called, the first,
     third, and fourth parameters will be passed on to
     `nnml-retrieve-headers', while the second parameter is set to the
     value of `nndir-current-group'.

`nnoo-import'
     This macro allows importing functions from backends.  It should be
     the last thing in the source file, since it will only define
     functions that haven't already been defined.

          (nnoo-import nndir
            (nnmh
             nnmh-request-list
             nnmh-request-newgroups)
            (nnml))

     This means that calls to `nndir-request-list' should just be passed
     on to `nnmh-request-list', while all public functions from `nnml'
     that haven't been defined in `nndir' yet should be defined now.

   Below is a slightly shortened version of the `nndir' backend.

     ;;; nndir.el --- single directory newsgroup access for Gnus
     ;; Copyright (C) 1995,96 Free Software Foundation, Inc.
     
     ;;; Code:
     
     (require 'nnheader)
     (require 'nnmh)
     (require 'nnml)
     (require 'nnoo)
     (eval-when-compile (require 'cl))
     
     (nnoo-declare nndir
       nnml nnmh)
     
     (defvoo nndir-directory nil
       "Where nndir will look for groups."
       nnml-current-directory nnmh-current-directory)
     
     (defvoo nndir-nov-is-evil nil
       "*Non-nil means that nndir will never retrieve NOV headers."
       nnml-nov-is-evil)
     
     (defvoo nndir-current-group "" nil nnml-current-group nnmh-current-group)
     (defvoo nndir-top-directory nil nil nnml-directory nnmh-directory)
     (defvoo nndir-get-new-mail nil nil nnml-get-new-mail nnmh-get-new-mail)
     
     (defvoo nndir-status-string "" nil nnmh-status-string)
     (defconst nndir-version "nndir 1.0")
     
     ;;; Interface functions.
     
     (nnoo-define-basics nndir)
     
     (deffoo nndir-open-server (server &optional defs)
       (setq nndir-directory
     	(or (cadr (assq 'nndir-directory defs))
     	    server))
       (unless (assq 'nndir-directory defs)
         (push `(nndir-directory ,server) defs))
       (push `(nndir-current-group
     	  ,(file-name-nondirectory (directory-file-name nndir-directory)))
     	defs)
       (push `(nndir-top-directory
     	  ,(file-name-directory (directory-file-name nndir-directory)))
     	defs)
       (nnoo-change-server 'nndir server defs))
     
     (nnoo-map-functions nndir
       (nnml-retrieve-headers 0 nndir-current-group 0 0)
       (nnmh-request-article 0 nndir-current-group 0 0)
       (nnmh-request-group nndir-current-group 0 0)
       (nnmh-close-group nndir-current-group 0))
     
     (nnoo-import nndir
       (nnmh
        nnmh-status-message
        nnmh-request-list
        nnmh-request-newgroups))
     
     (provide 'nndir)


File: gnus.info,  Node: Score File Syntax,  Next: Headers,  Prev: Backend Interface,  Up: A Programmers Guide to Gnus

Score File Syntax
-----------------

   Score files are meant to be easily parsable, but yet extremely
mallable.   It was decided that something that had the same read syntax
as an Emacs Lisp list would fit that spec.

   Here's a typical score file:

     (("summary"
       ("win95" -10000 nil s)
       ("Gnus"))
      ("from"
       ("Lars" -1000))
      (mark -100))

   BNF definition of a score file:

     score-file       = "" / "(" *element ")"
     element          = rule / atom
     rule             = string-rule / number-rule / date-rule
     string-rule      = "(" quote string-header quote space *string-match ")"
     number-rule      = "(" quote number-header quote space *number-match ")"
     date-rule        = "(" quote date-header quote space *date-match ")"
     quote            = <ascii 34>
     string-header    = "subject" / "from" / "references" / "message-id" /
                        "xref" / "body" / "head" / "all" / "followup"
     number-header    = "lines" / "chars"
     date-header      = "date"
     string-match     = "(" quote <string> quote [ "" / [ space score [ "" /
                        space date [ "" / [ space string-match-t ] ] ] ] ] ")"
     score            = "nil" / <integer>
     date             = "nil" / <natural number>
     string-match-t   = "nil" / "s" / "substring" / "S" / "Substring" /
                        "r" / "regex" / "R" / "Regex" /
                        "e" / "exact" / "E" / "Exact" /
                        "f" / "fuzzy" / "F" / "Fuzzy"
     number-match     = "(" <integer> [ "" / [ space score [ "" /
                        space date [ "" / [ space number-match-t ] ] ] ] ] ")"
     number-match-t   = "nil" / "=" / "<" / ">" / ">=" / "<="
     date-match       = "(" quote <string> quote [ "" / [ space score [ "" /
                        space date [ "" / [ space date-match-t ] ] ] ] ")"
     date-match-t     = "nil" / "at" / "before" / "after"
     atom             = "(" [ required-atom / optional-atom ] ")"
     required-atom    = mark / expunge / mark-and-expunge / files /
                        exclude-files / read-only / touched
     optional-atom    = adapt / local / eval
     mark             = "mark" space nil-or-number
     nil-or-number    = "nil" / <integer>
     expunge          = "expunge" space nil-or-number
     mark-and-expunge = "mark-and-expunge" space nil-or-number
     files            = "files" *[ space <string> ]
     exclude-files    = "exclude-files" *[ space <string> ]
     read-only        = "read-only" [ space "nil" / space "t" ]
     adapt            = "adapt" [ space "nil" / space "t" / space adapt-rule ]
     adapt-rule       = "(" *[ <string> *[ "(" <string> <integer> ")" ] ")"
     local            = "local" *[ space "(" <string> space <form> ")" ]
     eval             = "eval" space <form>
     space            = *[ " " / <TAB> / <NEWLINE> ]

   Any unrecognized elements in a score file should be ignored, but not
discarded.

   As you can see, white space is needed, but the type and amount of
white space is irrelevant.  This means that formatting of the score
file is left up to the programmer--if it's simpler to just spew it all
out on one looong line, then that's ok.

   The meaning of the various atoms are explained elsewhere in this
manual.


File: gnus.info,  Node: Headers,  Next: Ranges,  Prev: Score File Syntax,  Up: A Programmers Guide to Gnus

Headers
-------

   Gnus uses internally a format for storing article headers that
corresponds to the NOV format in a mysterious fashion.  One could
almost suspect that the author looked at the NOV specification and just
shamelessly *stole* the entire thing, and one would be right.

   "Header" is a severely overloaded term.  "Header" is used in RFC1036
to talk about lines in the head of an article (eg., `From').  It is
used by many people as a synonym for "head"--"the header and the body".
(That should be avoided, in my opinion.)  And Gnus uses a format
internally that it calls "header", which is what I'm talking about
here.  This is a 9-element vector, basically, with each header (ouch)
having one slot.

   These slots are, in order: `number', `subject', `from', `date',
`id', `references', `chars', `lines', `xref'.  There are macros for
accessing and setting these slots--they all have predictable names
beginning with `mail-header-' and `mail-header-set-', respectively.

   The `xref' slot is really a `misc' slot.  Any extra info will be put
in there.


File: gnus.info,  Node: Ranges,  Next: Group Info,  Prev: Headers,  Up: A Programmers Guide to Gnus

Ranges
------

   GNUS introduced a concept that I found so useful that I've started
using it a lot and have elaborated on it greatly.

   The question is simple: If you have a large amount of objects that
are identified by numbers (say, articles, to take a *wild* example)
that you want to callify as being "included", a normal sequence isn't
very useful.  (A 200,000 length sequence is a bit long-winded.)

   The solution is as simple as the question: You just collapse the
sequence.

     (1 2 3 4 5 6 10 11 12)

   is transformed into

     ((1 . 6) (10 . 12))

   To avoid having those nasty `(13 . 13)' elements to denote a
lonesome object, a `13' is a valid element:

     ((1 . 6) 7 (10 . 12))

   This means that comparing two ranges to find out whether they are
equal is slightly tricky:

     ((1 . 5) 7 8 (10 . 12))

   and

     ((1 . 5) (7 . 8) (10 . 12))

   are equal.  In fact, any non-descending list is a range:

     (1 2 3 4 5)

   is a perfectly valid range, although a pretty long-winded one.  This
is also legal:

     (1 . 5)

   and is equal to the previous range.

   Here's a BNF definition of ranges.  Of course, one must remember the
semantic requirement that the numbers are non-descending.  (Any number
of repetition of the same number is allowed, but apt to disappear in
range handling.)

     range           = simple-range / normal-range
     simple-range    = "(" number " . " number ")"
     normal-range    = "(" start-contents ")"
     contents        = "" / simple-range *[ " " contents ] /
                       number *[ " " contents ]

   Gnus currently uses ranges to keep track of read articles and article
marks.  I plan on implementing a number of range operators in C if The
Powers That Be are willing to let me.  (I haven't asked yet, because I
need to do some more thinking on what operators I need to make life
totally range-based without ever having to convert back to normal
sequences.)


File: gnus.info,  Node: Group Info,  Next: Emacs/XEmacs Code,  Prev: Ranges,  Up: A Programmers Guide to Gnus

Group Info
----------

   Gnus stores all permanent info on groups in a "group info" list.
This list is from three to six elements (or more) long and exhaustively
describes the group.

   Here are two example group infos; one is a very simple group while
the second is a more complex one:

     ("no.group" 5 (1 . 54324))
     
     ("nnml:my.mail" 3 ((1 . 5) 9 (20 . 55))
                     ((tick (15 . 19)) (replied 3 6 (19 . 3)))
                     (nnml "")
                     (auto-expire (to-address "ding@ifi.uio.no")))

   The first element is the group name as Gnus knows the group; the
second is the group level; the third is the read articles in range
format; the fourth is a list of article marks lists; the fifth is the
select method; and the sixth contains the group parameters.

   Here's a BNF definition of the group info format:

     info          = "(" group space level space read
                     [ "" / [ space marks-list [ "" / [ space method [ "" /
                     space parameters ] ] ] ] ] ")"
     group         = quote <string> quote
     level         = <integer in the range of 1 to inf>
     read          = range
     marks-lists   = nil / "(" *marks ")"
     marks         = "(" <string> range ")"
     method        = "(" <string> *elisp-forms ")"
     parameters    = "(" *elisp-forms ")"

   Actually that `marks' rule is a fib.  A `marks' is a `<string>'
consed on to a `range', but that's a bitch to say in pseudo-BNF.


File: gnus.info,  Node: Emacs/XEmacs Code,  Next: Various File Formats,  Prev: Group Info,  Up: A Programmers Guide to Gnus

Emacs/XEmacs Code
-----------------

   While Gnus runs under Emacs, XEmacs and Mule, I decided that one of
the platforms must be the primary one.  I chose Emacs.  Not because I
don't like XEmacs or Mule, but because it comes first alphabetically.

   This means that Gnus will byte-compile under Emacs with nary a
warning, while XEmacs will pump out gigabytes of warnings while
byte-compiling.  As I use byte-compilation warnings to help me root out
trivial errors in Gnus, that's very useful.

   I've also consistently used Emacs function interfaces, but have used
Gnusey aliases for the functions.  To take an example:  Emacs defines a
`run-at-time' function while XEmacs defines a `start-itimer' function.
I then define a function called `gnus-run-at-time' that takes the same
parameters as the Emacs `run-at-time'.  When running Gnus under Emacs,
the former function is just an alias for the latter.  However, when
running under XEmacs, the former is an alias for the following function:

     (defun gnus-xmas-run-at-time (time repeat function &rest args)
       (start-itimer
        "gnus-run-at-time"
        `(lambda ()
           (,function ,@args))
        time repeat))

   This sort of thing has been done for bunches of functions.  Gnus does
not redefine any native Emacs functions while running under XEmacs--it
does this `defalias' thing with Gnus equivalents instead.  Cleaner all
over.

   Of course, I could have chosen XEmacs as my native platform and done
mapping functions the other way around.  But I didn't.  The performance
hit these indirections impose on Gnus under XEmacs should be slight.


File: gnus.info,  Node: Various File Formats,  Prev: Emacs/XEmacs Code,  Up: A Programmers Guide to Gnus

Various File Formats
--------------------

* Menu:

* Active File Format::      Information on articles and groups available.
* Newsgroups File Format::  Group descriptions.


File: gnus.info,  Node: Active File Format,  Next: Newsgroups File Format,  Up: Various File Formats

Active File Format
..................

   The active file lists all groups that are available on the server in
question.  It also lists the highest and lowest current article numbers
in each group.

   Here's an excerpt from a typical active file:

     soc.motss 296030 293865 y
     alt.binaries.pictures.fractals 3922 3913 n
     comp.sources.unix 1605 1593 m
     comp.binaries.ibm.pc 5097 5089 y
     no.general 1000 900 y

   Here's a pseudo-BNF definition of this file:

     active      = *group-line
     group-line  = group space high-number space low-number space flag <NEWLINE>
     group       = <non-white-space string>
     space       = " "
     high-number = <non-negative integer>
     low-number  = <positive integer>
     flag        = "y" / "n" / "m" / "j" / "x" / "=" group


File: gnus.info,  Node: Newsgroups File Format,  Prev: Active File Format,  Up: Various File Formats

Newsgroups File Format
......................

   The newsgroups file lists groups along with their descriptions.  Not
all groups on the server have to be listed,  and not all groups in the
file have to exist on the server.  The file is meant purely as
information to the user.

   The format is quite simple; a group name, a tab, and the description.
Here's the definition:

     newsgroups    = *line
     line          = group tab description <NEWLINE>
     group         = <non-white-space string>
     tab           = <TAB>
     description   = <string>


File: gnus.info,  Node: Emacs for Heathens,  Next: Frequently Asked Questions,  Prev: A Programmers Guide to Gnus,  Up: Appendices

Emacs for Heathens
==================

   Believe it or not, but some people who use Gnus haven't really used
Emacs much before they embarked on their journey on the Gnus Love Boat.
If you are one of those unfortunates whom "`M-C-a'", "kill the region",
and "set `gnus-flargblossen' to an alist where the key is a regexp that
is used for matching on the group name" are magical phrases with little
or no meaning, then this appendix is for you.  If you are already
familiar with Emacs, just ignore this and go fondle your cat instead.

* Menu:

* Keystrokes::      Entering text and executing commands.
* Emacs Lisp::      The built-in Emacs programming language.


File: gnus.info,  Node: Keystrokes,  Next: Emacs Lisp,  Up: Emacs for Heathens

Keystrokes
----------

   * Q: What is an experienced Emacs user?

   * A: A person who wishes that the terminal had pedals.

   Yes, when you use Emacs, you are apt to use the control key, the
shift key and the meta key a lot.  This is very annoying to some people
(notably `vi'le users), and the rest of us just love the hell out of
it.  Just give up and submit.  Emacs really does stand for
"Escape-Meta-Alt-Control-Shift", and not "Editing Macros", as you may
have heard from other disreputable sources (like the Emacs author).

   The shift key is normally located near your pinky fingers, and are
normally used to get capital letters and stuff.  You probably use it all
the time.  The control key is normally marked "CTRL" or something like
that.  The meta key is, funnily enough, never marked as such on any
keyboards.  The one I'm currently at has a key that's marked "Alt",
which is the meta key on this keyboard.  It's usually located somewhere
to the left hand side of the keyboard, usually on the bottom row.

   Now, us Emacs people doesn't say "press the meta-control-m key",
because that's just too inconvenient.  We say "press the `M-C-m' key".
`M-' is the prefix that means "meta" and "C-" is the prefix that means
"control".  So "press `C-k'" means "press down the control key, and
hold it down while you press `k'".  "Press `M-C-k'" means "press down
and hold down the meta key and the control key and then press `k'".
Simple, ay?

   This is somewhat complicated by the fact that not all keyboards have
a meta key.  In that case you can use the "escape" key.  Then `M-k'
means "press escape, release escape, press `k'".  That's much more work
than if you have a meta key, so if that's the case, I respectfully
suggest you get a real keyboard with a meta key.  You can't live without
it.

