Viz GUI:how to get a control node to bend a straight arrow?

I remember searching for this a long time ago and have dark memories of finding how to do it, but I cannot find that information now and cannot remember how to get a control handle on an arrow in Viz so that that arrow can be bent. How is it done? Or did I just dream about finding out how to do it?

AFAICT control handles on edges are added by the Visualizer itself, you can’t do it yourself. I don’t know the exact algorithm but I infer that these handles are only added if an edge crosses several diagram layers (the drawing algorithm is essentially Sugiyama’s DAG drawing algorithm, which works by creating layers of nodes and drawing edges, adding a hidden node when an edge crosses over a layer). On the contrary, if an edge is only on a given layer or between two consecutive layers, I think no control point shall appear.