+become a combination orthogonal to the one it is part of.
+
+If this variable is t, 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.
+
+The value of this variable is also assigned to the combination limit of
+the new parent window. The combination limit of a window can be
+retrieved via the function `window-combination-limit' and altered by the
+function `set-window-combination-limit'. */);
+ Vwindow_combination_limit = Qnil;
+
+ DEFVAR_LISP ("window-persistent-parameters", Vwindow_persistent_parameters,
+ doc: /* Alist of persistent window parameters.
+This alist specifies which window parameters shall get saved by
+`current-window-configuration' and `window-state-get' and subsequently
+restored to their previous values by `set-window-configuration' and
+`window-state-put'.
+
+The car of each entry of this alist is the symbol specifying the
+parameter. The cdr is one of the following:
+
+nil means the parameter is neither saved by `window-state-get' nor by
+`current-window-configuration'.
+
+t means the parameter is saved by `current-window-configuration' and,
+provided its WRITABLE argument is nil, by `window-state-get'.