Doc fix for left-fringe and right-fringe parameters (Bug#6930)

* doc/lispref/frames.texi (Layout Parameters): Note the difference
between querying and setting parameters for left-fringe and
right-fringe.

1 files changed, 12 insertions, 9 deletions

diff --git a/doc/lispref/frames.texi b/doc/lispref/frames.texi
index a99782b95e..0c81718750 100644
--- a/doc/lispref/frames.texi
+++ b/doc/lispref/frames.texi
@@ -654,17 +654,20 @@ use the default width.
 @itemx right-fringe
 The default width of the left and right fringes of windows in this
 frame (@pxref{Fringes}).  If either of these is zero, that effectively
-removes the corresponding fringe.  A value of @code{nil} stands for
-the standard fringe width, which is the width needed to display the
-fringe bitmaps.
+removes the corresponding fringe.
+
+When you use @code{frame-parameter} to query the value of either of
+these two frame parameters, the return value is always an integer.
+When using @code{set-frame-parameter}, passing a @code{nil} value
+imposes an actual default value of 8 pixels.
 
 The combined fringe widths must add up to an integral number of
-columns, so the actual default fringe widths for the frame may be
-larger than the specified values.  The extra width needed to reach an
-acceptable total is distributed evenly between the left and right
-fringe.  However, you can force one fringe or the other to a precise
-width by specifying that width as a negative integer.  If both widths are
-negative, only the left fringe gets the specified width.
+columns, so the actual default fringe widths for the frame, as
+reported by @code{frame-parameter}, may be larger than what you
+specify.  Any extra width is distributed evenly between the left and
+right fringe.  However, you can force one fringe or the other to a
+precise width by specifying that width as a negative integer.  If both
+widths are negative, only the left fringe gets the specified width.
 
 @item menu-bar-lines
 The number of lines to allocate at the top of the frame for a menu