seeking howto -- split a high res display with two diff user desktop sessions

Is there some way to login as two different users and have their desktop sessions shared/split on a single hi-res display?

I know that there are utilities like 'screen' that split a shell session. I want to login and launch a desktop for one user. Then I want to split the display and login as a second, different user with their own desktop session.

My search attempts have not been successful. Likely, I'm not using the correct keywords to search for this feature.

Thanks in advance,
~~~ 0;-Dan