Prop1 in IGES TYPE 126

Hi,

Type 126 PROP1 states that: If the curve lies entirely within a unique plane, the planar flag (PROP1) is set to 1, otherwise it is set to 0. If it is set to 1, the plane normal (Parameters 14+A+4*K through 16+A+4*K) contain a unit vector normal to the plane containing the curve.

1. what is the unique plane referred here?
2. what kind of test could decide if the curve lies on this unique plane?

please correct me if I am wrong.

thanks.

jeff