Tags in DHTML pages quickly get cluttered with numerous on-some-event="fn(id)" attributes, making it nightmarish to maintain hand-coded pages. Instead bind elements and behaviours (events and functions) separately from tags. Microsoft introduced behaviours for Internet Explorer 5.5 for special effects in a page but their implementation uses non-standard additions (unsurprisingly) to CSS. Ben Nolan wrote a browser independent behaviour library and Lambda-the-ultimate forum has a discussion. Using CSS selectors to specify elements allows multiple HTML elements to have the same behaviour and multiple behaviours to be mapped to one HTML element (as long as the events don't overlap). Très cool indeed!