DesktopConfiguration

Starting with fvwm3, using RandR support, fvwm can manage each monitor connected to it independently. The DesktopCoonfiguration command tells fvwm3 how to manage the virtual desktop. The three supported modes are:

Fvwm splits its virtual desktop into both Pages and Desks. The FvwmPager module provides a miniature view of the desks and virtual pages.

Global

This is the default and traditional way of dealing with multiple monitors. They all move through the virtual pages and desks as a single group. In essence think of all monitors as a single big monitor that can view a given piece of the virtual desktop.

Per-Monitor

This allows controlling which page/desktop each monitor is on independently. In this case think of each monitor as having its own virtual desktop independent of each other, with the advantage you can move windows between monitors on different desks/pages.

Shared

This is similar to per-monitor mode, in that each monitor can move around the pages independently. The difference is the virtual desktops are shared across the monitors. This means, that only a single monitor can view a desk at a time. If you move a monitor to a desk that is currently being viewed another monitor, the two desks these monitors are viewing will be swapped. In other words all the windows in all pages across the same desk are swapped between the two monitors.