This gives the name of the Public Screen on which to open all TSMorph windows - default is the default public screen.
This parameter is not changed by Requester loaded projects.
It can be changed using the menu item (if reqtools.library is available), a requester is displayed allowing the input of the screen name, but any change is ignored until TSMorph is reloaded.
If CUSTOMMODE is supplied as well then a public screen of this name is opened.