One strategy for allowing multiple elements to respond to a click is called event capturing. With capturing, the event is first given to the most all-encompassing element, then to successively more specific ones.
The opposite strategy is called event bubbling. The event gets sent to the most specific element, and after this element has an opportunity to react, the event bubbles up to more general elements.
Unsurprisingly, different browser developers originally decided on different models for event propagation. The DOM standard that eventually developed thus specified that both strategies should be used: first the event is captured from general elements to specific ones, and then the event bubbles back up to the top of the DOM tree. Event handlers can be registered for either part of the process
Not all browsers have been updated to match this new standard, and in those that support capturing it typically must be specifically enabled.
— Learning jQuery 1.3