Function union_aabb 

pub fn union_aabb<'a>(
    boxes: impl IntoIterator<Item = &'a [Scalar; 3]>,
) -> Option<[Scalar; 3]>

The box around all of boxes (each a curve’s or a surface’s, see crate::nurb_curve::NurbCurve::aabb): per axis the union of theirs. None for no boxes.