Given the extremely open nature of the Action Sheets proposal, it's a little difficult to evaluate its strengths and weaknesses. On the other hand, the Cascading Action Sheets example has a little more substance to it, and therefore offers at least a few points to critique. One nice thing about CAS is that it uses CSS selectors, which most designers already know. This limits selections to those possible using CSS, but many would not find this to be a major flaw.
One potentially serious problem with Action Sheets is that all actions must be assigned from within an Action Sheet, using the system's selectors. In other words, it isn't possible to attach actions directly to elements in the way that styles can be assigned using the STYLE attribute in HTML 4.0 (or DHTML Behaviors, for that matter). Without the addition of a new attribute to HTML (ACTION comes to mind), this would never be possible. In XML, on the other hand, such an attribute could be defined in a document's DTD (document type definition) and employed without much trouble at all.
There is also no defined mechanism for determining where the actions fall in the cascade. Do they have more or less weight than styles, or are they in some way equivalent? The Note has nothing to say on this point, and this sort of behavior isn't really required by the Action System proposal.
Another potential problem: Since Internet Explorer has gone the DHTML Behaviors route, while Navigator has taken the Action Sheets approach, there is already a gap opening in behavior handling. Microsoft's documentation states that DHTML Behaviors are a developing technology and subject to change, but it's rare that a browser feature changes much after it's been deployed. The fear is that each browser will go its own way, once again forcing developers to juggle both sets of features in order to create "universal" pages.
Fortunately Action Sheets (and DHTML Behaviors) are XML documents, and this open framework would allow developers to employ these technologies without having to worry about tripping across proprietary landmines.
We must remember, of course, that the Action Sheets proposal is merely a W3C Note, and has as much official support from the W3C as the un-Noted DHTML Behaviors. Action Sheets could be drastically rewritten, perhaps to include aspects of Microsoft's DHTML Behavior technology, or even thrown out entirely. Nonetheless, it seems likely that even if Action Sheets don't become a standard, something like them will. As you might guess from the fact that both Netscape and Microsoft are working on their own solutions, the advantages of being able to separate behaviors from individual documents are far too great to ignore for long.
