code: private void generateLimitElement(XmlElement element) {
          XmlElement ifLimitNotNullElement = new XmlElement("if");
          ifLimitNotNullElement.addAttribute(new Attribute("test", "rows != null"));
  
          XmlElement ifOffsetNotNullElement = new XmlElement("if");
          ifOffsetNotNullElement.addAttribute(new Attribute("test", "offset != null"));
          ifOffsetNotNullElement.addElement(new TextElement("limit ${offset}, ${rows}"));
          ifLimitNotNullElement.addElement(ifOffsetNotNullElement);
  
          XmlElement ifOffsetNullElement = new XmlElement("if");
          ifOffsetNullElement.addAttribute(new Attribute("test", "offset == null"));
          ifOffsetNullElement.addElement(new TextElement("limit ${rows}"));
          ifLimitNotNullElement.addElement(ifOffsetNullElement);
  
          element.addElement(ifLimitNotNullElement);
      }
docs: 生成limit节点
  @param element