text: <===> input.scss
  @function test($pos) {
    @return test-#{$pos};
  }
  
  .foo {
    content: test(str-slice('scale-0', 7));   // Nope
    content: test-#{str-slice('scale-0', 7)}; // Yep
  }
  <===> output.css
  .foo {
    content: test-0;
    content: test-0;
  }
  