Click on the chart and use the right arrow key to follow the largest flow out of the current node, and the left arrow key to follow the largest flow back in. The up and down arrow keys walk the other nodes stacked in the same column. Each move announces the flow it was taken along — where it came from, how much ran along it, and what share of the node's output that was — rather than just the node it landed on. Press B for braille, T for text descriptions, and S to toggle sonification.
A row whose to is left out is an AnyChart "dropoff": the
chart draws a ribbon leaving the node and going nowhere. It names no
target, so it is not a flow and is left out of the reading — and because
the chart still draws it, highlighting is switched off for the whole chart
rather than pairing every later ribbon with the wrong flow.