>> Maybe you can come up with some advanced technique to do that but here I
 >> would have to define a variable to save the current (user provided)
 >> `split-window-preferred-function' and call the function I save there
 >> within the body of the function provided by dired.
 >
 > I'd use something like
 >
 >   (lexical-let ((oldfun split-window-preferred-function))
 >     (let ((split-window-preferred-function
 >            (lambda () (with-selected-window TOTO (funcall oldfun)))))
 >       BLABLA))

We probably need something like in the attached patch but my knowledge
of closures within Elisp is very limited.

 > The above coding should be close to "standard practice" for locally
 > rebinding a *-function variable.  The "extra variable" doesn't matter,
 > it's not like we count variables.
 >
 > Maybe what you're getting at is that we should make a hook to influence
 > the window-choice.  Maybe so.  But it doesn't seem urgent.

I was aiming at an extra variable to work around "advanced techniques"
like closures.  `lexical-let' doesn't even indent reasonably :-(

martin