Clicking the "Frobnicate This!" buttons will trigger the frobnicate event on the button.
As of jQuery 1.3, custom events bubble up to the parents, so a frobnicate event on the button will propagate to the div around it, unless it's blocked.
The green div responds to the frobnicate event by drawing a border around itself.
The red div doesn't respond to it, and thus, clicking on the "Frobnicate This!" button inside it does nothing.