Virtual Groups
--------------

   An "nnvirtual group" is really nothing more than a collection of
other groups.

   For instance, if you are tired of reading many small group, you can
put them all in one big group, and then grow tired of reading one big,
unwieldy group.  The joys of computing!

   You specify `nnvirtual' as the method.  The address should be a
regexp to match component groups.

   All marks in the virtual group will stick to the articles in the
component groups.  So if you tick an article in a virtual group, the
article will also be ticked in the component group from whence it came.
(And vice versa--marks from the component groups will also be shown in
the virtual group.)

   Here's an example `nnvirtual' method that collects all Andrea Dworkin
newsgroups into one, big, happy newsgroup:

     (nnvirtual "^alt\\.fan\\.andrea-dworkin$\\|^rec\\.dworkin.*")

   The component groups can be native or foreign; everything should work
smoothly, but if your computer explodes, it was probably my fault.

   Collecting the same group from several servers might actually be a
good idea if users have set the Distribution header to limit
distribution.  If you would like to read `soc.motss' both from a server
in Japan and a server in Norway, you could use the following as the
group regexp:

     "^nntp+some.server.jp:soc.motss$\\|^nntp+some.server.no:soc.motss$"

   This should work kinda smoothly--all articles from both groups should
end up in this one, and there should be no duplicates.  Threading (and
the rest) will still work as usual, but there might be problems with the
sequence of articles.  Sorting on date might be an option here (
see Selecting a Group..

   One limitation, however--all groups that are included in a virtual
group has to be alive (i.e., subscribed or unsubscribed).  Killed or
zombie groups can't be component groups for `nnvirtual' groups.

   If the `nnvirtual-always-rescan' is non-`nil', `nnvirtual' will
always scan groups for unread articles when entering a virtual group.
If this variable is `nil' (which is the default) and you read articles
in a component group after the virtual group has been activated, the
read articles from the component group will show up when you enter the
virtual group.  You'll also see this effect if you have two virtual
groups that contain the same component group.  If that's the case, you
should set this variable to `t'.  Or you can just tap `M-g' on the
virtual group every time before you enter it--it'll have much the same
effect.