Gives you control to perform actions when the control key and the mouse button is clicked in the same time. Something similar to selecting elements in Windows with ctrl+click.

Just change the event.ctrlKey to event.shiftKey to make it shift+click. If you don't get it don't worry the snippet contains the demo for shift+click too.

You may need to change the event.which though 1 = left click, 2 = middle click, 3 = right click(at least in firefox 1.5.0.5)