QML has always had it, as far as I know. It makes for a little pause when loading an application as the logic is compiled. I'm not sure what other markup langua

QML has always had it, as far as I know. It makes for a little pause when loading an application as the logic is compiled. I'm not sure what other markup languages have done this, though. They do have a Qt Quick compiler though which removes the need to JIT the user interface; maybe next release it'll see the light of day on the open-source side of things.