twitter/bootstrap — pull request #6068 by percyhanna (2012-11-29 20:54:51+00:00)
Title: Remove non-mixins from mixins.less

I was importing mixins.less for some of my own projects to use some of the mixins available to extend some themes. I found that including mixins.less would also add some style definitions at the top of my compiled CSS file due to some of the definitions in mixins.less not actually being mixins but instead they are definitions in themselves.

This approach allows @import-ing mixins.less without the added definitions that would already be defined in bootstrap.css, assuming you're also including that on your website.