The wire payload: a string for "json", a GeometryGraphEnvelope
for "object", a Uint8Array for "cbor".
Bytes of the wire payload (UTF-8 for JSON); 0 without one.
No payload and no refusal: a product with no Body representation.
World placement, as productPlacements gives it. The graph is already
in world coordinates: never apply this to it again.
One product's Body as a geometry graph, from
IfcModel.productGeometry.