I just realised that this project has been released under the mozilla github account — this (might) mean that it'll be actively maintained, and perhaps better documented than other libraries around.

:thumbsup: Looks really great

Right now, the AM site, Glen's site and am-grid. This is the first time we've shared what we've been working on.

Absolutely! The prefix is optional (but recommended). If you're comfortable with data attributes (or, they're required for some reason), thats cool too.

Performance of long CSS files isn't really the (major) concern —its how many _elements_ are being traversed (size of the dom) that really effects CSS-selector performance.

After a certain point the number of selectors does affect parsing time and selector matching time, in a very significant way.

Performance has improved a bit since this post but it's still relevant: http://perfectionkills.com/profiling-css-for-fun-and-profit-...

You could also use <video src="/path/to/vid.mp4" muted loop autoplay>

That's what sites do currently, but it's still not quite there yet, because it requires special markup and doesn't loop when you share the URL directly (I hope the latter can be fixed easily: https://bugzilla.mozilla.org/show_bug.cgi?id=1041238 https://code.google.com/p/chromium/issues/detail?id=395413).

Annoyingly GIF isn't supported as a source in <video> either, which adds extra complexity when you want to provide a proper fallback.

I don’t think the markup for `<video autoplay muted loop>` is an issue. These attributes exist for this use case.

That being said, video in CSS background is a legit feature request.

>doesn't loop when you share the URL directly

You can deal with that server-side by checking referrers and other headers and serving HTML.