It probably would be hard to diagram it in 3-dimensional space, much less two. But maybe we could do a table with the columns Start State, Event, New State, Notes. Perhaps we could create the source document in JSON format or something. It would be nice if we could convert it with code to RST, but also load it into a spreadsheet. So we could sort on either Start State or New State.
The problem with real-world state machines is that they don't really have a small number of discrete states. They have a state vector with multiple variables, with a huge number of potential states. An often-effective cheat is to make fake distinctions between events that really reflect state differences. For example, considering "receive bytes when buffer empty" and "receive bytes when buffer not empty" as distinct events. But maybe our state machine is so complex it would overwhelm this cheat strategy.
