docs: private static String badIndexMsg(int index, int size, String desc, Object... params) {
  		if (index < 0) {
  			return StrUtil.format("{} ({}) must not be negative", StrUtil.format(desc, params), index);
  		} else if (size < 0) {
  			throw new IllegalArgumentException("negative size: " + size);
  		} else { // index >= size
  			return StrUtil.format("{} ({}) must be less than size ({})", StrUtil.format(desc, params), index, size);
  		}
  	}