Return combination limit of window WINDOW.
If the return value is nil, child windows of WINDOW can be recombined
with WINDOW's siblings. A return value of t means that child windows of
WINDOW are never (re-)combined with WINDOW's siblings.
WINDOW must be a valid window. The return value is meaningful for
internal windows only.
(fn WINDOW)
If non-nil, splitting a window makes a new parent window.
The following values are recognized:
nil means splitting a window will create a new parent window only if the
window has no parent window or the window shall become part of a
combination orthogonal to the one it is part of.
`window-size' means that splitting a window for displaying a buffer
makes a new parent window provided `display-buffer' is supposed to
explicitly set the window's size due to the presence of a
`window-height' or `window-width' entry in the alist used by
`display-buffer'. Otherwise, this value is handled like nil.
`temp-buffer' means that splitting a window for displaying a temporary
buffer always makes a new parent window. Otherwise, this value is
handled like nil.
`display-buffer' means that splitting a window for displaying a buffer
always makes a new parent window. Since temporary buffers are
displayed by the function `display-buffer', this value is stronger
than `temp-buffer'. Splitting a window for other purpose makes a
new parent window only if needed.
t means that splitting a window always creates a new parent window. If
all splits behave this way, each frame's window tree is a binary
tree and every window but the frame's root window has exactly one
sibling.
Other values are reserved for future use.