Function port_seat_of 

pub fn port_seat_of(point: &PortPoint, scene: &SceneMap) -> (Frame, Vec<String>)

The FRAME a connection point’s placement is an offset in.

Its origin is where pointRef seats the point (the part origin when there is none) and its x_axis is the direction that seats it: directionRef when the point names one, else whatever pointRef implied, else +X. The point’s own transform is then read IN this frame — position along its three axes, rotationEuler composed onto its basis — so a point seated on a face can be nudged 2 mm off it and turned 30 degrees on it without the reference being lost.

With NO reference at all the seat is the world frame, and a local offset in the world frame is an absolute placement: that is the case every document written before the seat existed is in, and it reads exactly as it did.

Problems are collected, never fatal. A reference that resolves to nothing leaves that half of the seat at its default and says so by name.