public static List<XmlElementDescriptor> getRequiredSubTags(XmlElementDescriptor selected) {
    XmlElementsGroup topGroup = selected.getTopGroup();
    if (topGroup == null) return Collections.emptyList();
    return computeRequiredSubTags(topGroup);
  }
public static List<XmlElementDescriptor> getRequiredSubTags(XmlElementDescriptor selected)