For example, you can use a behavior to add expanding and collapsing functionality to an HTML list without any script on the page. Internet Explorer 5 provides a number of benefits for both users and developers. Users will have a faster and more robust browser. Developers will have more control than ever. A page can be created that is easy to view in any tool.
Some tools just make it a lot easier.
I don't quite understand how to write it. One of the best ways to get started is to look at the samples and try to understand how they work. No official word yet on when they'll release, but probably around the end of the year. We're also starting to see greater adoption on the Internet. We do not have support for behaviors and several other technologies on the Macintosh yet.