code: private Expression parseAtomList() {
          Expression exp = parseAtom();
          if (!tokenizer.current().isSymbol(",")) {
              return exp;
          }
  
          ValueList atomList = new ValueList(true);
          atomList.add(exp);
          while (tokenizer.current().isSymbol(",")) {
              tokenizer.consume();
              atomList.add(parseAtom());
          }
  
          return atomList;
      }
docs: /*
  Parses an atom. This is either an identifier ("bold"), a number (15px), a string ('OpenSans'), a color
  (#454545) or another expression in braces.