code: public void push( PageFlowController pageFlow, HttpServletRequest request )
      {
          ActionInterceptorContext interceptorContext = ActionInterceptorContext.getActiveContext( request, true );
          if ( interceptorContext != null )
          {
              ActionInterceptor interceptor = interceptorContext.getOverridingActionInterceptor();
              InterceptorForward originalForward = interceptorContext.getOriginalForward();
              String actionName = interceptorContext.getActionName();
              _stack.push( new PushedPageFlow( pageFlow, interceptor, originalForward, actionName ) );
          }
          else
          {
              _stack.push( new PushedPageFlow( pageFlow ) );
          }
          
          // Tell the page flow that it is on the nesting stack.
          pageFlow.setIsOnNestingStack( true );
          
          // To ensure that this attribute is replicated for session failover.
          ensureFailover( request, getServletContext() );
      }
docs: Push a page flow onto the stack of nested page flows in the session.
  
  @param pageFlow the page flow to push.
  @param request the current HttpServletRequest.