The solution is to specify which HTML / CSS / etc standard we coded for, and, horror of horrors, the browser could interpret correctly? (Maybe a variable for whether you want a browser to “do its best” if it doesn’t fully support the standard you specified.) This plus new HTML and CSS specs that tie up ambiguous loose ends would address the browser compatibility issues that currently double the time required for web projects.

I believe it all comes down to progression of the field. If some people are sitting behind at IE7 and CSS 2, what difficulties will that cause when we’ve reached CSS 4 or 5? It just doesn’t seem like we’re doing ourselves or anyone else any favors by allowing developers, even inexperienced ones, to freeze in the development of their skills and work. We need to look and move forward, not back.

That statement fairly well sums up my concerns too.

Although, I also find myself considering the approach that Adobe (and formerly Macromedia) have taken with Flash. The Flash Player does support a great many (maybe all?) legacy versions of Flash, meaning that if you built a Flash site many years back (I have sites going back almost a decade) they still work today. I am very grateful I have never had to rework these sites, since during that time Flash has had 3 radical revisions to its programming language, and I would literally have to start from scratch! While there there are no doubt some Flash developers “stuck in the past” as far as their programming skills go, I don’t think there is any evidence that backwards compatibility has been a roadblock for the Flash development community as a whole.

This is precisely the part of this idea I have difficulties with. If the developer is not forced to update their website for the current, or last previous as I am suggesting, version of the browser, then there will be some websites stuck at 7, 8, 9 ,10, etc. until the changes are not “internally ‘breaking changes’”. The only result will be browser that have to be able to render all previous versions until the versions that feature only slight differences like Chris mentions.

I think your last comment hit the nail on the head with, “My suspicion is that many legacy sites won’t be upgraded until they break.” It would solve the problem for many to allow one previous version to automatically opt out to, but will force an update deadline. This will allow plenty of time for the developers who are aware of the problem to get their sites up to speed. For all the others that won’t be aware of the problem until their site breaks, they need that push to move forward. Otherwise, they are precisely the people that will be holding us at version 7 when the current version is 20.

I believe it all comes down to progression of the field. If some people are sitting behind at IE7 and CSS 2, what difficulties will that cause when we’ve reached CSS 4 or 5? It just doesn’t seem like we’re doing ourselves or anyone else any favors by allowing developers, even inexperienced ones, to freeze in the development of their skills and work. We need to look and move forward, not back.

As you point out, this approach would give web authors additional time to fix their sites. However, if an author has not learned of the version targeting changes by the time IE8 is released, why should we assume they will be aware of them by the time IE9 is launched? My suspicion is that many legacy sites won’t be upgraded until they break. That may be when IE9 is released, or if Microsoft take the “freezing” approach, it may happen many versions from now.

Chris Wilson from the IE team has indicated that rather than IE becoming bloated with multiple rendering engines, he sees that eventually the problem will go away. From an interview with Sitepoint:

SP: Now, with this developer opt-in model that Internet Explorer and, if it goes into the HTML spec, all browsers will eventually adopt, are browsers over time going to have, you know, five, six, seven, ten, eighteen different rendering modes for each version of the spec that’s released over time, or will this tendency of the differences to tend towards zero over time mean that one day this can go away?

Chris Wilson: I think that my personal hope, certainly, is that one day this gets to go away, that the differences between browser versions are not what we call internally ‘breaking changes.’

I’m not sure if we can infer from Chris’ statement whether IE7 will be the default rendering engine in IE9+, or not…