> Subtopic one (in topic one) will be different as Subtopic one (in topic two) in most real cases, probably. A clear example is scientific literature where each chapter could have a 'results' section, maybe with different subsection names.

I agree. In fact, I set out to make it this way initially. It's either more difficult to implement this, or I don't know the dot language well enough - probably the latter.

I did a dirty hack to do exactly what you're saying for a scientific paper. I modified the code to check if the current line/topic/node was already mentioned in the output string. If so, I tacked on a random number to the node name. Yuck.

Ideally, there would be option to preserve a strict tree-like architecture in better way.