EVENT FLOW

When development for the fourth generation of web browsers began (Internet Explorer 4 and Netscape Communicator 4), the browser development teams were met with an interesting question: What part of a page owns a specific event? To understand the issue, consider a series of concentric circles on a piece of paper. When you place your finger at the center, it is inside of not just one circle but all of the circles on the paper. Both development teams looked at browser events in the same way. When you click on a button, they concluded, you're clicking not just on the button but also on its container and on the page as a whole.

Event flow describes the order in which events are received on the page, and interestingly, the Internet Explorer and Netscape development teams came up with an almost exactly opposite concept of event flow. Internet Explorer would support an event bubbling flow, whereas Netscape Communicator would support an event capturing flow.

Event Bubbling

The...