docs: public List<CmsContainerPageElementPanel> getModelGroups() {
  
          final List<CmsContainerPageElementPanel> result = Lists.newArrayList();
  
          processPageContent(new I_PageContentVisitor() {
  
              public boolean beginContainer(String name, CmsContainer container) {
  
                  return true;
              }
  
              public void endContainer() {
  
                  // do nothing
              }
  
              public void handleElement(CmsContainerPageElementPanel element) {
  
                  if (element.isModelGroup()) {
                      result.add(element);
                  }
              }
          });
          return result;
      }