Constant PATH_POINT_AMBIGUOUS 

pub const PATH_POINT_AMBIGUOUS: &str = "a curve path piece bounded by a point that several parameters of its curve name (the curve \
     passes through it more than once, or it is the seam of a closed curve other than a circle \
     or an ellipse)";

The input a point bound of a curve path piece (#304) is refused for when several parameters of the curve name it: a curve that passes through it more than once, or the seam of a closed curve other than a circle or an ellipse (whose angle runs round).