code: protected static void setShell(CareWebShell shell) {
          if (getShell() != null) {
              throw new RuntimeException("A CareWeb shell instance has already been registered.");
          }
  
          ExecutionContext.getPage().setAttribute(Constants.SHELL_INSTANCE, shell);
      }
docs: Sets the active instance of the CareWeb shell. An exception is raised if an active instance
  has already been set.
  
  @param shell Shell to become the active instance.