code: private String formatDefaultValue(Object value) {
      if (value instanceof Boolean) {
        return ((Boolean) value) ? "true" : "false";
      }
  
      if (value instanceof Number) {
        return value.toString();
      }
  
      if (value instanceof Collection) {
        return formatCollectionValue((Collection) value);
      }
  
      String string = value.toString();
  
      if (string.startsWith("$")) {
        return string;
      }
  
      return SassString.escape(string);
    }
docs: Format a default value for libsass function signature.
  
  @param value The default value.
  @return The formated default value.