@only directive

Idea is to define a block which will be used in particular selector if rule is true. And all other properties in whole selector should be skipped. As a simple example: main.scss

body {
    background: #000;
    @only $forIE8 {
        background: #FFF;
    }
    @only $forIE9 {
        background: #CCC;
    }
}

ie8.scss

$forIE8: true;
@import "main";

ie9.scss

$forIE9: true;
@import "main";

all.scss

$forIE8: false;
@import "main";

Output: ie8.css

body {
  background: #FFF;
}

ie9.css

body {
  background: #CCC;
}

all.css

body {
  background: #000;
}

[wheeyls]

FWIW, I thought this directive would be helpful as well. I’ve written a postcss plugin based on this syntax here: https://github.com/wheeyls/postcss-only-directive.

[nex3]

@if and @else are sufficient for this use case.