code: public Xml addContent(String text) {
          if(current == null) {
              throw new XmlModelException("Content can not be attached as root element: " + text);
          }
          Content content = new Content(text);
          content.setParent(current);
          current.addChildElement(content);
          return this;
      }
docs: Add a {@code Content} element. The cursor will point to the parent element after calling this method since child
  elements that are of the Content type can't have child elements.
  @param text character data
  @return {@code Xml}