Hello, in a zen page sometimes I find document.getElementbyId("ID") to set a propertybut also zen("ID").setPr.... So what is the real difference and limitations of each?

Until what version of HTML and CSS can I use on zen pages? 

Does anyone know how to get the closing tab/menu changing event in a CSP? I've tried the JS "OnBeforeUnload" already but it seems the browsers aren't allowing it anymore. I need to show a pop-up that holds the user if trying to get away before completing the stage.