OS2.0+
You can open a Public Screen using the CLI-Option "-e" or the
Tooltype "SCREEN". Optionally you can pass some arguments:
depth: (default 2) Number of Bitplanes being used
displayID: (default $8000) DisplayID looked up in sys:WBStartup/Mode_Names
overscan: (default 1) Overscan type. 1=text, 2=standard, 3=maximum
title: (default ZShell) Case sensitive name of Public Screen

To get your window open there, you have to add ".../SCREEN ZShell" to your
window-description.

Examples for CLI-Start:
ZShell "-wCON:////Shell/CLOSE/SCREEN ZShell" -e                   Try it 
ZShell "-wCON:1/10/640/390/Shell/CLOSE/SCREEN ZShell" -e1/$8004   Try it 
ZShell "-wCON:////Shell/CLOSE/SCREEN Super" -e3/$8000/2/Super     Try it 

Example for Workbench-Start:
SCREEN=3/$8000/1/ZShell-Screen
WINDOW=CON:1/10/640/190/Shell/CLOSE/SCREEN ZShell-Screen          Try it 

Example for a fullsize ZShell on its own PAL-screen:
SCREEN=
WINDOW=CON:1/4/640/253//NOBORDER/NOSIZE/BACKDROP/SCREEN ZShell    Try it