For example, suppose you want to write a selector that matches the outer selector *and* an element selector. You could write a mixin like this one that uses the [`selector-unify()` function][] to combine `&` with a user's selector. [`selector-unify()` function]: ../functions/selectors#selector-unify <% example do %> @mixin unify-parent($child) { @at-root #{selector-unify(&, $child)} { @content; } } .wrapper .field { @include unify-parent("input") { /* ... */ } @include unify-parent("select") { /* ... */ } } === @mixin unify-parent($child) @at-root #{selector-unify(&, $child)} @content .wrapper .field @include unify-parent("input") /* ... @include unify-parent("select") /* ... <% end %>