'window-divider-default-places', 'window-divider-default-bottom-width'
and 'window-divider-default-right-width'.
+*** When a window is shrunk horizontally its margins are no more removed
+automatically. Rather, Emacs refuses to split or resize windows when
+this would cause margins to no more fit into the width reserved for the
+corresponding window. An application can override this behavior for a
+particular window by setting that window's 'min-margins' parameter. As
+a consequence, the application becomes fully responsible for trimming
+the margin sizes of that window and any window inheriting these margins.
+
*** The window displaying the '*Completions*' buffer with minibuffer
completion candidates is now shown at the bottom of the selected
frame. The size of that window is always as large as required to