1<===> input.scss
2@mixin foo($option: 'foo') {
3     // Create a unique, random placeholder to store styles
4    $placeholder : $option + random(9999);
5
6    // Store the styles in the placeholder
7    @at-root %#{$placeholder} {
8        content: 'foo';
9    }
10
11    @at-root {
12        .bar {
13            @extend %#{$placeholder};
14        }
15    }
16}
17
18@mixin bar($option) {
19    @include foo($option);
20}
21
22.foo {
23    @include bar('baz');
24}
25<===> output.css
26.bar {
27  content: 'foo';
28}
29
30<===> output-dart-sass.css
31.bar {
32  content: "foo";
33}
34