onBounce
The instruction(s) to be executed are placed within quotes. This event handler will execute the instruction(s) when the scrolling text of a marquee has reached the edge of the element area.

The following example will display text of your choosing in a message box when the scrolling text of a marquee has reached the edge of the element area:
onBounce="msgWindow.document.write('-- Insert text message here --')"
This Event Handler is used with the following:

MARQUEE