This read-only object reports the unprintable margin from the leading edge of the medium as it passes through the marking engine, measured in the units set by prtMarkerAddressabilityUnit. An admin needs this figure when designing full-bleed or near-edge layouts, since content placed within the value reported here plus the other three margins is guaranteed to print correctly on every supported interpreter. For example, if this margin is nonzero, a page layout with content flush to the very top edge would be clipped or shifted, so the admin would build layouts that respect this offset.