Indicates if any of the sub-systems in the device are
not idle. The I/O source sub-system is considered not
idle if there is unprocessed PDL data in the device.
The PDL processing sub-system is considered not idle if
the device is processing a print job. The print engine
destination sub-system is considered not idle if media
is moving (i.e. the device is printing). [other text
here describing what causes the other sub-systems to be
considered not idle].