Not completely sure since I haven't tested it out yet, but I'd assume that it would only pop up when you're adjusting the screen while a DVD is inserted. It sounds like something that could be adjusted when you're watching a movie or something.
Lucy, it looks like the DVD option is only available outside the US.
My CT 200h is fully loaded and I looked through the manual. It looks like for our cars, our button is labeled "CD", which means we can only play CDs and MP3 CDs. In the UK, for example, their button is labeled "DISC", which means they can play DVDs as well when parked. BOO!!!!!!
No way the USA would ever allow a DVD player to be on the flip up LCD screen in front of the driver. We have enough accidents here from distracted drivers. Bring along a DVD player or iPad to watch videos but not while you're driving please!
DVDs are playable on the front screen in most every other Lexus in North America with ML systems. As a safety feature, they can only normally be played while the car is stationary and with the parking brake on.
However, here are many work-arounds ("hacks") to defeat this feature. Not saying that it should be done, but it can.