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(gnus)Undo

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Undo
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   It is very useful to be able to undo actions one has done.  In normal
Emacs buffers, it's easy enough--you just push the `undo' button.  In
Gnus buffers, however, it isn't that simple.

   The things Gnus displays in its buffer is of no value whatsoever to
Gnus--it's all just data designed to look nice to the user.  Killing a
group in the group buffer with `C-k' makes the line disappear, but
that's just a side-effect of the real action--the removal of the group
in question from the internal Gnus structures.  Undoing something like
that can't be done by the normal Emacs `undo' function.

   Gnus tries to remedy this somewhat by keeping track of what the user
does and coming up with actions that would reverse the actions the user
takes.  When the user then presses the `undo' key, Gnus will run the
code to reverse the previous action, or the previous actions.  However,
not all actions are easily reversible, so Gnus currently offers a few
key functions to be undoable.  These include killing groups, yanking
groups, and changing the list of read articles of groups.  That's it,
really.  More functions may be added in the future, but each added
function means an increase in data to be stored, so Gnus will never be
totally undoable.

   The undoability is provided by the `gnus-undo-mode' minor mode.  It
is used if `gnus-use-undo' is non-`nil', which is the default.  The
`M-C-_' key performs the `gnus-undo' command, which should feel kinda
like the normal Emacs `undo' command.