This feedback was provided as part of the accessibility review #105:

The example graph uses 'ASCII art' to convey its structure. This isn't accessible to ATs.

This should be regarded as low priority compared to the other issues; if we get the time, we may submit a PR. My current best thought on how to make the graph (which is in this case a tree) more accessible would be to express it as a nested list, which would share the tree structure, but we would root the list on the output, so it would be 'backwards' relative to the visual version. It could be done via SVG (using a technique Léonie Watson proposed) though we'd want to test this out before making anyone do work!