#define WM_XBUTTONDOWN (WM_MOUSEWHEEL + 1)
#define WM_XBUTTONUP (WM_MOUSEWHEEL + 2)
#endif /* WM_XBUTTONDOWN */
+#ifndef WM_MOUSEHWHEEL
+#define WM_MOUSEHWHEEL (WM_MOUSEWHEEL + 4)
+#endif /* WM_MOUSEHWHEEL */
#define WM_EMACS_START (WM_USER + 1)
#define WM_EMACS_KILL (WM_EMACS_START + 0)