Some months ago we discussed help for isearch-forward/backward. I tried 
several alternatives at that time, but did not send in any patch. The 
attached patch is a simple way to give help. It simply defines C-h and 
f1 to call isearch-mode-help and allows scrolling of the help with keys 
that are bound to scroll-other-window[-down]. This was the only 
alternative I could get to work in a nice manner as far as I remember now.

I also found some small errors which I tried to correct. This was 
something with the isearch-ring but I can not remember the details right 
now. I included that also in the patch however.

I renamed search-ring-update to isearch-ring-update which seems more 
consistent. Maybe that should not be done if that breaks something?

BTW I think there may be some useful key definitions missing in the 
help. Could you for example not switch the direction with C-r? Should 
not that be added to the help?