Pavane, my friend, you've set for yourself a formidable task. But you knew that.

I assume you've studied all the available tab programs including the various existing tab kludges for ABC and widely used programs like Power Tab Editor and TablEdit Tablature Editor. As I'm sure you've noticed, each of these implimentations has one or more flaws that tend to cause the user to long for something better. They're all useable in many situations, they just don't always support one's current requirement or way of working.

My chief complaint about some tab implementations is a lack of accurate rhythm notation. It's great to see that you intend to overcome that. The only tab output I've seen that is useable includes a properly typeset score above the tab. Usually both score and tab are needed to accurately express the rhythm of the tab (note durations, rests, triplets, ties, slurs, etc.).

But, in my opinion, computed tab—tab that merely computes the location of the note for a specific tuning and number of strings—is nearly worthless. Except as a programming exercise, I really don't think such an effort is worthy of your time. There must be a way for the transcriber to specify both string and fret for each tab note and still specify an ABC chord name (e.g., "F°") that might not compute from either the ABC notation or the tab.

Good luck. Let us know how it's going.

      - Mark