The margin, in units identified by prtMarkerAddressabilityUnit,
from the leading edge of the medium as the medium flows
through the marking engine with the side to be imaged
facing the observer. The leading edge is the North edge
and the other edges are defined by the normal compass
layout of directions with the compass facing the
observer. Printing within the area bounded by all four
margins is guaranteed for all interpreters. The value
(-2) means unknown.