I’m looking for input on a project that will benefit us all. I have been hard at work creating a semi-open source WP theme. The quick explanation is this: it will be free to use, given you are granted permission. The idea behind this is simple: Quality control. We don’t want bad websites built on one of the best available theme frameworks. Designers will be granted access to the theme but will not be given permission to incorporate it in large-scale deployments (for example, you start a hosting company and yell “FREE THEMES FOR EVERYBODY!” …that’s a no-go.) And, of course, I’ll be starting a theme store where designers can sell their themes built on the framework which will have, dare I say, the best commission structure around.
However, I would use something like Selectivizr, but only if important stuff was breaking, and I couldn’t fix it by using only CSS1 selectors.
Modernizr is useful also, in situations where you have to do something completely different if a feature isn’t supported.
If it was necessary, things like border-box polyfills I would use, because they are important and can break a site if not supported.
> We don’t want bad websites built on one of the best available theme frameworks.
> There is ABSOLUTELY no way you can possibly stop people from building bad websites.
I have to agree with that. Thats the internet – a blessing and a cure at the same time.
Regarding you initial question: Loading polyfills for small presentational stuff like rounded corners or box shadows is not recommended most of the time. Also, using polyfills for stuff like flexbox can be tricky, but it’s possible of course. But well, you haven’t even said you want to do that.
I would incorporate Modernizr (of course a custom build that only holds the detects you need) for sure, it’s a great tool if used right. Regarding Polyfills: I can’t comment on eCSStender as I havent worked with it. selectivizr can come in really useful, but maybe try first if you can get away without it somehow. PIE is also pretty good, but again: You don’t need if for presentational stuff. That being said, I am a big fan of the [webshims lib](http://afarkas.github.com/webshim/demos/index.html “webshims lib”). Having used it a couple of times and I can tell you: Together with Modernizr for feature detection and loading, this is a true blessing.
Simply do your tests, if they fail load the webshims polyfill file that acts as “base” for the lib. Depending on what you want to polyfill, the polyfills are loaded async, meaning that even if it takes a bit to load, the page isn’t blocked and it is only loaded what is needed I believe.