New version - Ninja2 + touchwrap
Older version -Ninja
When mouse/touch overlap instance with this behavior, the instance will be shown (visible = true), otherwise instance will be hidden (visible = false).
It can be used in scrolling button at boundary, like the arrow in this picture.
<img src="http://i1081.photobucket.com/albums/j352/rexrainbow1/file-2.jpg" border="0">
(Image: gonzdevour)