i did a lot of test about “position_material”, searched internet about UV mapping

The pt_array must contain 2, 4, 6 or 8 points. The points are used in pairs to tell where a point in the texture image is positioned on the Face. The first point in each pair is a 3D point in the model. It should be a point on the Face. The second point in each pair of points is a 2D point that gives the (u,v) coordinates of a point in the image to match up with the 3D point.

still uncertain and confused of this API , is there any other documents can tell me more?

i know vector as array works the same, but what does each number of array mean?

please help me