1<===> options.yml
2---
3:todo:
4- sass/libsass#2987
5
6<===> input.scss
7.m__exhibit-header--medium {
8    @extend #{&}--plain;
9    &--plain {
10        font-size: --&;
11    }
12}
13<===> output.css
14.m__exhibit-header--medium--plain, .m__exhibit-header--medium {
15  font-size: -- .m__exhibit-header--medium--plain;
16}
17