<===> input.scss
.bracketed-lists {
  empty: [];
  single: [foo];
  multiple: [foo, bar];
  nested: [[foo], [[bar, baz]]];
  space-separated: [foo bar baz];
  trailing-comma: [foo, bar,];

  // List functions treat it like a list.
  nth-comma: nth([foo, bar], 2);
  nth-space: nth([foo bar], 2);
  comma-separator: list-separator([foo, bar]);
  space-separator: list-separator([foo bar]);

  // List functions preserve bracketedness.
  set-nth: set-nth([foo, bar, baz], 2, qux);
  append: append([foo, bar], baz);
  append-with-separator: append([foo, bar], baz, $separator: space);

  // Inspection produces valid input. This also verifies that nested lists of
  // various sorts are parsed properly.
  inspect-empty: inspect([]);
  inspect-simple: inspect([foo, bar]);
  inspect-nested-bracketed: inspect([[foo]]);
  inspect-nested-unbracketed: inspect([(foo bar)]);
  inspect-nested-unbracketed-comma: inspect([foo bar,]);
  inspect-nested-unbracketed-singleton: inspect([(foo,)]);
}

<===> output.css
.bracketed-lists {
  empty: [];
  single: [foo];
  multiple: [foo, bar];
  nested: [[foo], [[bar, baz]]];
  space-separated: [foo bar baz];
  trailing-comma: [foo, bar];
  nth-comma: bar;
  nth-space: bar;
  comma-separator: comma;
  space-separator: space;
  set-nth: [foo, qux, baz];
  append: [foo, bar, baz];
  append-with-separator: [foo bar baz];
  inspect-empty: [];
  inspect-simple: [foo, bar];
  inspect-nested-bracketed: [[foo]];
  inspect-nested-unbracketed: [(foo bar)];
  inspect-nested-unbracketed-comma: [foo bar,];
  inspect-nested-unbracketed-singleton: [(foo,)];
}