docs: public static CmsXmlContainerPage unmarshal(
          CmsObject cms,
          Document document,
          String encoding,
          EntityResolver resolver) {
  
          CmsXmlContainerPage content = new CmsXmlContainerPage(cms, document, encoding, resolver);
          // call prepare for use content handler and return the result
          return (CmsXmlContainerPage)content.getHandler().prepareForUse(cms, content);
      }