Completion Guru needed (next/prev)

["David R. Favor" <dfavor@xxxxxxxxxxxxxx>]

I'm trying to create a next/prev completion facility to quickly
traverse complicated directory hierarchies.

Here is an example hierarchy:

   ./src
   ./src/tools
   ./src/lib
   ./src/client
   ./src/server
   ./src/server/a
   ./src/server/b
   ./src/server/c
   ./doc
   ./doc/unix
   ./doc/html
   ./doc/ps
   ./info

Typing cd-SPACE-TAB begins completion of the directories [src doc info]. Here's
what I'm trying to do.

NEXT completion:

If src is currently seleted, normally it requires hitting BACKSPACE-TAB-TAB to
begin selecting directories [client lib server tools]. I would like to be able
to do this by hitting the shortcut SHIFT-TAB.

PREVIOUS completion:

If src/server/ is currently selected, I would like to be able to hit CNTL-TAB
to go back to selecting [client lib server tools]

Suggestions would be appreciated.

Thanks.