Agreed that this would be a sensible improvement to current browsers. But on its own it doesn't really improve the user-experience much. You'll still have to sit there twiddling your thumbs while the page downloads in the background. We need XMLHttpRequest (or something like it).
(Again, recall the disclaimer in my original post: "no, I'm not against all that is AJAX. I'm really just posting about the quoted-and-discussed issue.")
My original post was regarding the concept that AJAX techniques provide a solution for the annoyance of needing to fully redraw a page just to see relatively minor content changes. The AJAX solution to this problem is a hack that prevents the browser from throwing away the current page and starting from scratch. If the browser itself were smart enough to do this when it detected substantively similar blocks of HTML, this hack would not be necessary.
Let's assume that for most websites, the latency of the network roundtrip and the latency of the drawing time are the big time sinks, and that the size of the raw (compressed) HTML for the page itself (i.e., not images etc.) has a minimal impact on the time of the request. Given these assumptions, an XMLHttpRequest-based approach will take roughly the same amount of elapsed time as a "normal" HttpRequest. So, the benefit that AJAX brings to the table for these types of situations is that it provides a workaround to the fact that browsers *do* redraw everything from scratch pretty much every time. The user still has to twiddle thumbs while waiting for the XMLHttpRequest downloads in the background, and the elapsed time for that download is on the same order of the elapsed time for the full-page (sans images etc.) download. The benefit is that browsers do a somewhat-decent job of letting bits of JavaScript do some page-redrawing.
However, this UI benefit comes at a cost -- back buttons don't always work quite as expected, development / maintenance time is typically longer, compatibility is often sacrificed, etc.
If someone were to spend the time to optimize a browser to deal well with loading pages that are vastly similar to their predecessors, all HTML-based websites would immediately benefit (when accessed with that browser). As I had attempted to make clear in my original post, there is clearly still a place for AJAX techniques, as the HTML primitives are, well, primitive, and do not really allow for much fancy stuff (except for everyone's favorite, of course, the venerable BLINK tag).
-Patrick
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Patrick Linskey
http://solarmetric.com