Mark all as unread

[Lars Tobias Borsting]

I'm doing some cleaning up and I would like to mark all articles in a
buffer as unread. It is quite easy to obtain instructions on how to make
all articles read, but very difficult to find out how to do the
opposite. Strange.

How do I:
1. mark all articles in the summary buffer between the mark and the
   point unread?
2. mark all articles in the summary buffer as unread?
3. mark all articles in a group as unread?

Thanks for any help!
--
Lars Tobias Borsting