visionmedia/rework — pull request #3 by sbrekken (2012-09-04 09:47:22+00:00)
Title: Handle existing media queries and supplied vendor prefixes in at2x plugin.

This patch improves the at2x plugin by adding support for existing media queries and vendor prefixes.

Arguably one could nest media query rules but [nesting only works in CSS3 compliant browsers](http://stackoverflow.com/a/11747166/669360).

In addition the patch makes sure only `background` and `background-image` declarations are processed since including all declarations with url values would add unnecessary media queries to things like fonts etc.