Fix a recent documentation change

* doc/emacs/frames.texi (Mouse Commands): More detailed
description of how tilting the mouse-wheel works.

* lisp/mwheel.el (mouse-wheel-tilt-scroll)
(mouse-wheel-flip-direction): Fix the wording of doc strings.
(Bug#39979)

2 files changed, 15 insertions, 8 deletions

diff --git a/doc/emacs/frames.texi b/doc/emacs/frames.texi
index 16205e6e0c3..7a583b96bbd 100644
--- a/doc/emacs/frames.texi
+++ b/doc/emacs/frames.texi
@@ -217,11 +217,15 @@ default bound to scrolling with the @key{Ctrl} modifier.
 @vindex mouse-wheel-tilt-scroll
 @vindex mouse-wheel-flip-direction
 Emacs can also support horizontal scrolling if your mouse's wheel can
-be tilted, or your touchpad supports it.  This feature is off by
-default; the variable @code{mouse-wheel-tilt-scroll} turns it on.  If
-you'd like to reverse the direction of horizontal scrolling, customize
-the variable @code{mouse-wheel-flip-direction} to a non-@code{nil}
-value.
+be tilted, or if your touchpad supports it.  This feature is off by
+default; the variable @code{mouse-wheel-tilt-scroll} turns it on, if
+you customize it to a non-@code{nil} value.  By default, tilting the
+mouse wheel scrolls the window's view horizontally in the direction of
+the tilt: e.g., tilting to the right scrolls the window to the right,
+so that the text displayed in the window moves horizontally to the
+left.  If you'd like to reverse the direction of horizontal scrolling,
+customize the variable @code{mouse-wheel-flip-direction} to a
+non-@code{nil} value.
 
 When the mouse pointer is over an image, scrolling the mouse wheel
 with the @key{Ctrl} modifier scales the image under the mouse pointer.
diff --git a/lisp/mwheel.el b/lisp/mwheel.el
index 79977ef8640..317f2cd8edd 100644
--- a/lisp/mwheel.el
+++ b/lisp/mwheel.el
@@ -145,7 +145,7 @@ face height."
 ;;; For tilt-scroll
 ;;;
 (defcustom mouse-wheel-tilt-scroll nil
-  "Enable horizontal scrolling via mouse or touchpad.
+  "Enable horizontal scrolling by tilting mouse wheel or via touchpad.
 Also see `mouse-wheel-flip-direction'."
   :group 'mouse
   :type 'boolean
@@ -153,8 +153,11 @@ Also see `mouse-wheel-flip-direction'."
 
 (defcustom mouse-wheel-flip-direction nil
   "Swap direction of `wheel-right' and `wheel-left'.
-This inverts the direction of horizontal scrolling.  Also see
-`mouse-wheel-tilt-scroll'."
+By default, `wheel-right' scrolls the text to the right,
+and `wheel-left' scrolls in the other direction.
+If this variable is non-nil, it inverts the direction of
+horizontal scrolling by tilting the mouse wheel.
+Also see `mouse-wheel-tilt-scroll'."
   :group 'mouse
   :type 'boolean
   :version "26.1")