diff --git a/main.lua b/main.lua
index d2aec13..1be4308 100644
--- a/main.lua
+++ b/main.lua
@@ -202,6 +202,12 @@ function App.wheelmoved(dx,dy)
   if on.mouse_wheel_move then on.mouse_wheel_move(dx,dy) end
 end
 
+function App.mousefocus(in_focus)
+  if Mode == 'error' then return end
+  Cursor_time = 0  -- ensure cursor is visible immediately after it moves
+  if on.mouse_focus then on.mouse_focus(in_focus) end
+end
+
 function App.focus(in_focus)
   if Mode == 'error' then return end
   if in_focus then
diff --git a/reference.md b/reference.md
index 09ee003..6c228c4 100644
--- a/reference.md
+++ b/reference.md
@@ -97,6 +97,11 @@ two categories.
   right. Positive values for `dy` indicate upward movement.
   (Based on [LÖVE](https://love2d.org/wiki/love.wheelmoved).)
 
+* `on.mouse_focus(in_focus)` -- called when the mouse pointer moves on or off
+  the app window. `in_focus` will be `true` when mouse comes within the window
+  area, and `false` when it goes off.
+  (Based on [LÖVE](https://love2d.org/wiki/love.mousefocus).)
+
 * `on.keychord_press(chord, key)` -- called when you press a key-combination.
   Provides in `key` a string name for the key most recently pressed ([valid
   values](https://love2d.org/wiki/KeyConstant)). Provides in `chord` a