code: protected static CmsPrincipalSelectExtension getInstance() {
  
          A_CmsUI ui = A_CmsUI.get();
          CmsPrincipalSelectExtension instance = (CmsPrincipalSelectExtension)ui.getAttribute(
              CmsPrincipalSelectExtension.class.getName());
          if (instance == null) {
              instance = new CmsPrincipalSelectExtension(ui);
              ui.setAttribute(CmsPrincipalSelectExtension.class.getName(), instance);
          }
          return instance;
      }
docs: Returns the principal select extension instance for the current UI.<p>
  
  @return the instance