Documentation parts of the scroll fix.

src/xdisp.c (syms_of_xdisp) <scroll-conservatively>: Document the
 threshold of 100 lines for never-recentering scrolling.
 doc/emacs/display.texi (Auto Scrolling): Document the limit of 100
 lines for never-recentering scrolling with `scroll-conservatively'.

doc/emacs/ChangeLog

@@ -1,3 +1,9 @@
+2011-03-30  Eli Zaretskii  <eliz@gnu.org>
+
+	* display.texi (Auto Scrolling): Document the limit of 100 lines
+	for never-recentering scrolling with `scroll-conservatively'.
+	(Bug#6671)
+
 2011-03-12  Eli Zaretskii  <eliz@gnu.org>
 
 	* msdog.texi (Windows HOME): Fix the wording to clarify how Emacs sets

doc/emacs/display.texi

@@ -183,7 +183,20 @@ visible portion of the text.
 if you set @code{scroll-conservatively} to a small number @var{n},
 then if you move point just a little off the screen (less than @var{n}
 lines), Emacs scrolls the text just far enough to bring point back on
-screen.  By default, @code{scroll-conservatively} is@tie{}0.
+screen.  By default, @code{scroll-conservatively} is@tie{}0.  If you
+set @code{scroll-conservatively} to a large number (larger than 100),
+Emacs will never center point as result of scrolling, even if point
+moves far away from the text previously displayed in the window.  With
+such a large value, Emacs will always scroll text just enough for
+bringing point into view, so point will end up at the top or bottom of
+the window, depending on the scroll direction.
+
+@vindex scroll-step
+  The variable @code{scroll-step} determines how many lines to scroll
+the window when point moves off the screen.  If moving by that number
+of lines fails to bring point back into view, point is centered
+instead.  The default value is zero, which causes point to always be
+centered after scrolling.
 
 @cindex aggressive scrolling
 @vindex scroll-up-aggressively
@@ -204,6 +217,9 @@ down.  The value specifies how far point should be placed from the
 bottom of the window; thus, as with @code{scroll-up-aggressively}, a
 larger value is more aggressive.
 
+  These two variables are ignored if either @code{scroll-step} or
+@code{scroll-conservatively} are set to a non-zero value.
+
 @vindex scroll-margin
   The variable @code{scroll-margin} restricts how close point can come
 to the top or bottom of a window.  Its value is a number of screen

src/ChangeLog

@@ -1,3 +1,8 @@
+2011-03-30  Eli Zaretskii  <eliz@gnu.org>
+
+	* xdisp.c (syms_of_xdisp) <scroll-conservatively>: Document the
+	threshold of 100 lines for never-recentering scrolling.
+
 2011-03-29  Eli Zaretskii  <eliz@gnu.org>
 
 	* xdisp.c (try_scrolling): When scrolling down aggressively,

src/xdisp.c

@@ -13003,7 +13003,10 @@ enum
   SCROLLING_NEED_LARGER_MATRICES
 };
 
-/* If scroll-conservatively is more than this, never recenter.  */
+/* If scroll-conservatively is more than this, never recenter.
+
+   If you change this, don't forget to update the doc string of
+   `scroll-conservatively' and the Emacs manual.  */
 #define SCROLL_LIMIT 100
 
 static int
@@ -26605,6 +26608,10 @@ If point moves off-screen, redisplay will scroll by up to
 onto the screen again.  If that cannot be done, then redisplay
 recenters point as usual.
 
+If the value is greater than 100, redisplay will never recenter point,
+but will always scroll just enough text to bring point into view, even
+if you move far away.
+
 A value of zero means always recenter point if it moves off screen.  */);
   scroll_conservatively = 0;