Given all this, wouldn't it be nice to have a system by which scripts could be defined in a manner similar to stylesheets? A setup where you could, say, define a generic behaviors document for your entire site, and simply link to that document from every page you maintain? If you said "yes," you're not alone. Programmers at Netscape and Microsoft have had the same thought.
The thinking at Netscape is described in a W3C Note titled Action Sheets: A Modular Way of Defining Behavior for XML and HTML. As a W3C Note, it is subject to change, and doesn't actually represent a direction by the W3C. The Note describes a possible approach which is open for public comment - a commendable move on Netscape's part - but may never come to pass. Or, if it does, it may be in a drastically modified form. In any case, it could be some time before Action Sheets become a working part of Navigator.
Meanwhile, Microsoft has been working on its own solution. DHTML Behaviors (nee Scriptlets) do some of the things that Netscape's Action Sheets propose, and they're available with the preview release of IE5. If you're interested in learning more about DHTML Behaviors, consult the Microsoft Site Builder Network.
Since there's as yet no place for you to see what Action Sheets can do, let's take a look at what Netscape has in store for them.