Document `scroll-bar-adjust-thumb-portion'.

1 files changed, 11 insertions, 0 deletions

diff --git a/doc/emacs/frames.texi b/doc/emacs/frames.texi
index d2c25b9dc05..3f4d6b12704 100644
--- a/doc/emacs/frames.texi
+++ b/doc/emacs/frames.texi
@@ -930,6 +930,17 @@ or disable the scroll bars (@pxref{Resources}).  To control the scroll
 bar width, change the @code{scroll-bar-width} frame parameter
 (@pxref{Frame Parameters,,, elisp, The Emacs Lisp Reference Manual}).
 
+@vindex scroll-bar-adjust-thumb-portion
+@cindex overscrolling
+If you're using Emacs on X (with GTK+ or Motif), you can customize the
+variable @code{scroll-bar-adjust-thumb-portion} to control
+@dfn{overscrolling} of the scroll bar, i.e. dragging the thumb down even
+when the end of the buffer is visible.  If its value is
+non-@code{nil}, the scroll bar can be dragged downwards even if the
+end of the buffer is shown; if @code{nil}, the thumb will be at the
+bottom when the end of the buffer is shown.  You can not over-scroll
+when the entire buffer is visible.
+
 @node Drag and Drop
 @section Drag and Drop
 @cindex drag and drop