Units as the parser resolved them. null only for a source that declares none — which a renderable TIN cannot be (LXML009), so null here means the document carries no numeric surface at all.
null
True when an operator supplied the unit for an undeclared source (§2.1).
LandXML may declare a different unit for elevation than for plan.
Units as the parser resolved them.
nullonly for a source that declares none — which a renderable TIN cannot be (LXML009), sonullhere means the document carries no numeric surface at all.