A coordinate system: an origin and three axes at right angles. A Plane fits a Frame input as its own axes.
An input that takes a Frame also takes a Plane.
Where the frame's three axes meet.
The affine map from this frame's local coordinates to world coordinates.
The frame's unit X direction.
The plane spanned by X and Y; its normal is the Z axis.
The plane spanned by X and Z; its normal is the Y axis.
The frame's unit Y direction.
The plane spanned by Y and Z; its normal is the X axis.
The frame's unit Z direction.
Items that are each a Frame. One Frame wired where a list is taken counts as a list of one.