JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

To capture more than one event, you should bitwise OR ( | ) the desired event masks together.
For example, to capture all click, dblClick, and blur events you might use
document.captureEvents(Event.CLICK | Event.DBLCLICK | Event.BLUR);
Turning off event capture is carried out analogously. You invoke the releaseEvents() method of
the appropriate object, passing the bitmask of the events to release as the argument. To turn
off event capturing of blur and click events at the Document level, you use
document.releaseEvents(Event.BLUR | Event.CLICK);
Event Propagation and Routing
Because Netscape propagates events top-down, handlers at a higher level in the document‘s
object tree always have the opportunity to handle an event before those at a lower level. If you
have instructed the Window and the Document to capture click events, for example, the
Window will capture the event because it is higher up the document object hierarchy.
Sometimes, however, a handler at a higher level might wish to not handle a particular event.
For example, you might be capturing all clicks at the Document level in order to handle all
button clicks in a single place. But the handler might receive a click event that wasn‘t on a
button, and therefore you may wish the event to continue on its journey to its intended target (a
link, for example).
To let an event proceed along down the hierarchy, a handler invokes the routeEvent() method
with the event it is processing as the argument. As an example, consider that you might want to
process clicks in a special manner if the user has the ALT key depressed.
You might capture clicks at the Window level, examine the Event, and pass it along to be
handled by lower-level handlers if the ALT key isn‘t depressed.
function handleClicks(event)
{
}
if (event.modifiers & Event.ALT_MASK)
{
}
else
// do something special because they have ALT depressed
routeEvent(event);
window.captureEvents(Event.CLICK);
window.onclick = handleClicks;
An occasionally useful aspect of routeEvent() is that it returns the value that the handler
eventually processing the object returns. Because of this, handlers higher up the hierarchy can