Document restrictions when setting window margins, fringes or scroll bars

* src/window.c (Fset_window_margins, Fset_window_fringes)
(Fset_window_scroll_bars): In doc-strings tell that a window
must be large enough to accommodate fringes, sroll bars and
margins of the desired size.
* doc/lispref/display.texi (Fringe Size/Pos, Scroll Bars)
(Display Margins): Tell that windows must be large enough to
accommodate fringes, sroll bars and margins of the desired
size.

1 files changed, 9 insertions, 2 deletions

diff --git a/src/window.c b/src/window.c
index 7b879d0e1eb..04183abb7c5 100644
--- a/src/window.c
+++ b/src/window.c
@@ -7076,7 +7076,9 @@ reserve for the left marginal area.  Optional third arg RIGHT-WIDTH
 does the same for the right marginal area.  A nil width parameter
 means no margin.
 
-Return t if any margin was actually changed and nil otherwise.  */)
+Leave margins unchanged if WINDOW is not large enough to accommodate
+margins of the desired width.  Return t if any margin was actually
+changed and nil otherwise.  */)
   (Lisp_Object window, Lisp_Object left_width, Lisp_Object right_width)
 {
   struct window *w = set_window_margins (decode_live_window (window),
@@ -7158,11 +7160,14 @@ the left fringe.  Optional third arg RIGHT-WIDTH specifies the right
 fringe width.  If a fringe width arg is nil, that means to use the
 frame's default fringe width.  Default fringe widths can be set with
 the command `set-fringe-style'.
+
 If optional fourth arg OUTSIDE-MARGINS is non-nil, draw the fringes
 outside of the display margins.  By default, fringes are drawn between
 display marginal areas and the text area.
 
-Return t if any fringe was actually changed and nil otherwise.  */)
+Leave fringes unchanged if WINDOW is not large enough to accommodate
+fringes of the desired width.  Return t if any fringe was actually
+changed and nil otherwise.  */)
   (Lisp_Object window, Lisp_Object left_width,
    Lisp_Object right_width, Lisp_Object outside_margins)
 {
@@ -7287,6 +7292,8 @@ horizontal scroll bar: bottom, nil, or t where nil means to not display
 a horizontal scroll bar on WINDOW and t means to use WINDOW frame's
 horizontal scroll bar type.
 
+If WINDOW is not large enough to accommodate a scroll bar of the
+desired dimension, leave the corresponding scroll bar unchanged.
 Return t if scroll bars were actually changed and nil otherwise.  */)
   (Lisp_Object window, Lisp_Object width, Lisp_Object vertical_type,
    Lisp_Object height, Lisp_Object horizontal_type)