// The client event TabMovingStart takes two parameters sender and e
// sender is the object which is raising the event
// e is the TabMovingEventArgs
function WebTab1_TabMovingStart(sender, e) {
//Gets the index of the tab item involved in the event as an integer
var tabIndex = e.get_tabIndex();
//Gets the visible index of the moving tab as an integer
var tabVisibleIndex = e.get_tabVisibleIndex();
//Assuming you have a label called labelOutput on the form
var label = $get('labelOutput');
if (tabIndex == 2)
//Cancels the TabMovingStart event if tab index is 2
e.set_cancel(true);
else
label.innerHTML = "Moving start for tab with index '" + tabIndex + "'...";
}