The fourth generation of browsers, primarily Internet Explorer 4 and Netscape 4, introduced a new way of assigning event handlers by using what are now referred to as DOM Level 0 event handlers. Think of a "level" as a version; these event handlers are called DOM Level 0 event handlers because they existed before any W3C DOM standard. Yet all browsers support them. Even to this day, DOM Level 0 event handlers are widely used and are an integral part of many web applications.
DOM Level 0 event handlers are properties ...