public final Side getDrawerSideShown() {
        return drawerSideShown.get();
    }
Returns a map of all overlays, which have previously been opened, with their corresponding
model object {@link WorkbenchOverlay}.

@return a map of all overlays, which have previously been opened, with their corresponding
model object {@link WorkbenchOverlay}.
workbenchfx-core/src/main/java/com/dlsc/workbenchfx/Workbench.java