The red region is a 3D off-axis asphere. The purple region is a transitional blend from the central 3D surface, to the outer '2D' edge segments.
Slow tool servos: Some surfaces can become very steep or mathematically 'illegal'. You now specify a 'cutoff', at which point DIFFSYS adds a curved corner and a flat at the edge.
Micro-lens arrays: aspheric, any diameter, spacing, and grid size.