Constant PATH_POINT_OFF_CURVE 

pub const PATH_POINT_OFF_CURVE: &str = "a curve path piece bounded by a point that does not lie on its curve within the joint \
     tolerance";

The input a point bound of a curve path piece (#304) is refused for when it does not lie on the piece’s curve within the joint tolerance 1e-9 * max(1, |p|): a provider never projects it onto the curve.