+// This bell implementation shows the visual bell image asynchronously
+// from the rest of Emacs. This is done by adding a NSView to the
+// superview of the Emacs window and removing it using a timer.
+//
+// Unfortunately, some Emacs operations, like scrolling, is done using
+// low-level primitives that copy the content of the window, including
+// the bell image. To some extent, this is handled by removing the
+// image prior to scrolling and marking that the window is in need for
+// redisplay.
+//
+// To test this code, make sure that there is no artifacts of the bell
+// image in the following situations. Use a non-empty buffer (like the
+// tutorial) to ensure that a scroll is performed:
+//
+// * Single-window: C-g C-v
+//
+// * Side-by-windows: C-x 3 C-g C-v
+//
+// * Windows above each other: C-x 2 C-g C-v
+