A 4x4 matrix that is applied to 3d coordinates for perspective. After this tranformation, the coordinates must be (x,-y,-z,z/p) in the reference frame where the viewer is at (0,0,0) and the screen at z=-p. One can instead provide a real number p, which is equivalent to placing the screen centered at z=0 and the viewer at (0,0,p). Only has an effect if in the outermost VectorGraphics object.
The object Perspective is a symbol.