>> Remains the question whether `split-window-preferred-function' should
 >> always operate on the selected window or have a window argument.  AFAICT
 >> nothing speaks for the window argument but the fact that people may have
 >> customized this already.  Omitting the window argument would allow users
 >> to put `split-window-vertically' directly as value of
 >> `split-window-preferred-function' without having to delve any deeper.
 >
 > I agree it would make sense to operate on the selected-window rather
 > than pass an explicit window argument.

Unfortunately, this will create the following problem: Suppose a user
wants to

(1) always split the selected window instead of the largest or LRU one,

(2) never split the selected window (as Drew points out in another
thread), or

(3) base her decision on whether a window shall be split on which window
was selected at the time `display-buffer' was called.

In any of these cases calling `split-window-preferred-function' with the
window to split selected will obscure the identity of the selected
window and make the desired customization impossible.  So we should
probably leave the current behavior alone.  The attached patch just
makes sure that `split-window-preferred-function' gets always called and
provides the standard options requested earlier.

martin