The query doesn't target 'screen' media but it uses the `@screen-*` variables as reference.

I also think, that the naming is misleading. `.screen-sm()` should cover only small screens while `.screen-sm-max()` should cover small screens and below. There should also be a third mixin `.screen-sm-min()` which covers small screens an above. Same for medium screen queries...

I made a [revision of my previous gist](https://gist.github.com/simbo/9427230) to clarify what i mean. I think you just adopted the names from the first dirty version. This revision also contains some `.screen()` mixins to quickly assign rules to multiple media queries.