Bug#989029: info: prev-line and scroll-backward are buggy on gnuplot.info

[Gavin Smith <gavinsmith0123@gmail.com>]

On Sat, Nov 12, 2022 at 12:40:11PM +0100, Vincent Lefevre wrote:
> But "down" is the reverse of "up". So, if you know all the "up"
> relations, you can deduce all the "down" relations, i.e. all the
> children. Then the issue is to sort the children, but I suppose
> that this could be done by looking at the "next" and "prev"
> relations among the children.

Yes in theory, but not easily done.

One possible improvement is to check the Up pointers when going down
the menus, and not going down if the Up pointer doesn't match the current node.