Of course my "look-up" in the IDE:
revIDENewMainstack max(<yourWidth>,400),max(<yourHeight>,400)
is quick and dirty compared to the clever plugin-solution of Klaus:
http://lists.runrev.com/pipermail/use-livecode/2017-July/239883.html
Sorry Klaus. I overlooked your post. I really write too much and read
too fast here. I'll better stop it now for a couple of months or so ...