emacs-27 ef5744a: Improve docs for horizontal scrolling with mouse and touchpad (Bug#39979)

[Noam Postavsky]

branch: emacs-27
commit ef5744a988f299c1b8b4726ee0d5bf9c1c1074f5
Author: İ. Göktuğ Kayaalp <address@hidden>
Commit: Noam Postavsky <address@hidden>

    Improve docs for horizontal scrolling with mouse and touchpad (Bug#39979)
    
    * lisp/mwheel.el (mouse-wheel-tilt-scroll,
    mouse-wheel-flip-direction): Improve docstrings.
    * doc/emacs/frames.texi (Mouse Commands): Mention touchpads.
---
 doc/emacs/frames.texi | 9 +++++----
 lisp/mwheel.el        | 7 +++++--
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/doc/emacs/frames.texi b/doc/emacs/frames.texi
index 002297c..16205e6 100644
--- a/doc/emacs/frames.texi
+++ b/doc/emacs/frames.texi
@@ -217,10 +217,11 @@ 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.  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 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.
 
 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 56150c8..79977ef 100644
--- a/lisp/mwheel.el
+++ b/lisp/mwheel.el
@@ -145,13 +145,16 @@ face height."
 ;;; For tilt-scroll
 ;;;
 (defcustom mouse-wheel-tilt-scroll nil
-  "Enable scroll using tilting mouse wheel."
+  "Enable horizontal scrolling via mouse or touchpad.
+Also see `mouse-wheel-flip-direction'."
   :group 'mouse
   :type 'boolean
   :version "26.1")
 
 (defcustom mouse-wheel-flip-direction nil
-  "Swap direction of `wheel-right' and `wheel-left'."
+  "Swap direction of `wheel-right' and `wheel-left'.
+This inverts the direction of horizontal scrolling.  Also see
+`mouse-wheel-tilt-scroll'."
   :group 'mouse
   :type 'boolean
   :version "26.1")