Topic Topology
--------------

   So, let's have a look at an example group buffer:

     Gnus
       Emacs -- I wuw it!
            3: comp.emacs
            2: alt.religion.emacs
         Naughty Emacs
          452: alt.sex.emacs
            0: comp.talk.emacs.recovery
       Misc
            8: comp.binaries.fractals
           13: comp.sources.unix

   So, here we have one top-level topic, two topics under that, and one
sub-topic under one of the sub-topics.  (There is always just one (1)
top-level topic).  This topology can be expressed as follows:

     (("Gnus" visible)
      (("Emacs -- I wuw it!" visible)
       (("Naughty Emacs" visible)))
      (("Misc" visible)))

   This is in fact how the variable `gnus-topic-topology' would look
for the display above.  That variable is saved in the `.newsrc.eld'
file, and shouldn't be messed with manually--unless you really want to.
Since this variable is read from the `.newsrc.eld' file, setting it in
any other startup files will have no effect.

   This topology shows what topics are sub-topics of what topics
(right), and which topics are visible.  Two settings are currently
allowed--`visible' and `invisible'.