public static @NotNull String writeChildren(@NotNull Element element, @NotNull String lineSeparator) throws IOException {
    StringWriter writer = new StringWriter();
    for (Element child : element.getChildren()) {
      writeElement(child, writer, lineSeparator);
      writer.append(lineSeparator);
    }
    return writer.toString();
  }
public static @NotNull String writeChildren(@NotNull Element element, @NotNull String lineSeparator)