He specified vector graphics, charting, animations, and layers. Those certainly can jazz up a site, but I wonder: How many sites really need all that? I'd consider this optional, but a big bonus.
Meriaz asked for internationalization and localization. That's a must only for sites that aren't limited to a single language and country.
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Security? I agree absolutely, but I think that it's so important that you should require it of every software component you use and every piece of code you write. Not every open source library has undergone a full security review, although some have. The enterprise-class products usually have, since the vendors expect customers to care about security.
Meriaz mentioned pace of development, meaning documentation, tools, and support. These are often, but not always, clear differentiators between open source projects and commercial solutions. I demand support from a commercial product, and I'm willing to pay for it because of the development time saved, and because providing it costs the vendor real money. I expect commercial documentation to be complete, up-to-date, and well-organized, although I'm often disappointed; I expect open source documentation to be cursory and an afterthought, although I'm sometimes pleasantly surprised. Tools that truly speed up development are worth paying for, although they're often available gratis.
Before I started researching this article, I had a preconceived notion that one of the distinguishing features of enterprise AJAX would be support for various servers in addition to the client libraries. Several of the enterprise AJAX packages do have extra support for specific server frameworks: For example, Backbase has additional support for JSF, Spring, JSP/Struts, and Java Data Services. On further thought, however, this isn't necessarily the case: Once you have a robust asynchronous callback mechanism, a flexible data format (such as XML or JSON), and support for the data format on both the client and server, you don't absolutely require special support for any given server built into the client.
Behind the browser
Another industry executive, Isomorphic founder and CTO Charles Kendrick, told me two reasons why his customers adopt his product rather than FOSS AJAX: the desire for an integrated solution, and the desire to be insulated from browser idiosyncrasies. The integrated solution argument is basically Meriaz's complete, extendable components library. Kendrick's additional point about this is that allowing developers to cobble together different solutions can be a minefield without serious (and expensive) integration testing.
His emphasis on using the framework to insulate the developer from cross-browser issues is a big one. Kendrick said, "I personally think eliminating this problem is the No. 1 thing that an enterprise AJAX platform should deliver."