I cannot make this work as a button on the border--clicking on it does nothing at all. I have Preferences / File Displays / Border / Set file display to source when border buttons are used turned on.
@ifset:SOURCE=Left
Go DRIVEBUTTONS=fixed,cdrom,network,removable,hideempty,mtp openinleft
@ifset:else
Go DRIVEBUTTONS=fixed,cdrom,network,removable,hideempty,mtp openinright