Disclaimer: I worked on the Microsoft Ajax 4.0 template engine, so my criteria are of course heavily influenced by our own design. Templates are a data rendering method that server-side developers have enjoyed since the old days of classic ASP and PHP. The idea was quite simple (add code blocks and dynamic expressions directly into HTML markup) but it revolutionized web development, which before that relied on the opposite method (spitting HTML from CGI code). On the client-side, the browser provides two ways to generate HTML: innerHTML and the DOM API. Template rendering is of course possible, but only using a JavaScript library. To be honest, one should mention XSLT here, which is standard and widely supported but whose somewhat unusual syntax...
Last week, we shipped the first preview for the Ajax work we're doing in ASP.NET 4.0 under the simple form of a simple script file (release and debug versions). This should show how much emphasis this release puts on the client-side. As a matter of facts, I'll use a plain HTML file here instead of an ASPX file to make it perfectly clear that everything here (except for the web service that provides the data) runs on the client. One of the scenarios we're trying to improve is updating parts of the page with new data without a postback (in other words, Ajax). That's a scenario you could implement in a number of manners. First, you could put an UpdatePanel control around your server rendering of the data and be done with it. That...