[xwiki-users] Query field in XWiki.WatchListClass object

Hello, I'd like to subscribe for Watch list email notification for my full XWiki. I know that I can subscribe space per space, but it is too long and I want to setup this later on user creation. So, I take a look on objects attached to my page and I see that there is third way to subscribe: QUERY. But I found nothing about what QUERY should look like! Can somebody provide a sample? Regards, Arnaud.