Yes, I am very familiar with Tramlink. The door buttons are surrounded by green LEDs which flash once a door button has been pressed (accompanied by 4 red LEDs when the button is pressed). As mentioned elsewhere, when these are flashing the doors on that side will all automatically open, even if the driver chooses only to unlock the doors, which is a rare occurrence nowadays. However it still happens and that is one of the reasons that when I come in to wimbledon and I am stood near the doors, I will always mash the button to ensure that even if the driver chooses only to release the door, I will still be able to get away quickly. When the doors are released the LEDs are a solid green, and when the button is pushed, they will open (á la National Rail). As for closing, normally they will stay open until the doors are closed by the driver, but on some trams, particularly at terminii and long stops, the doors will start ot closae automatically after a period of time (á la S Stock) but these will not be coordinated, I think it is done by how much time has passed by since the door was last used. The door can still be opened until the light goes out. As you mention as well, there is a selective re-open, which opens the far door at the end of the selected car so any latecomers can run on to the tram through the door often without using their oyster card!