First, ABC was initially developed to be able to transfer music formation in ASCII format, since the earliest computers really weren't graphically oriented. In addition, its initial purpose was for the easy transmission of "folk" tunes.

I agree with Jack Campin that the proper interpretation of

A:
B:

would be AABB. In ABC, any end repeat is considered to refer back to the closest of a begin repeat, a previous end repeat, or the beginning. Therefore, the end repeat for B would refer back to the end repeat for A (the closest of the three possible repeat points) and cause the B section to be repeated.

There seems to be an attitude in this thread that composers of "serious" music (read "classical") must be THE definitive sources for music notation rules. This, to me, seems a bit elitist and even flies in the face of history. Musical notation has been a long evolving process and the total body of music produced would be rife with exceptions to the "rule." Even in my performance of "serious" music for the recorder, I would expect that the notation would make proper use of "D.C." or "D.S." to direct me to repeat other than back to the first measure of the current section, whether a begin repeat existed or not.

I also agree with Jack that AbcMus is an excellent program. Since I use a PC, I output my AbcMus files to midi which I then open in NoteWorthy Composer, so I can't comment on his recommendation for abcm2ps.

Just to be fair, I did download and try ABC Navigator 2. Its output of an A:B: tune was AABB, correct in my opinion. However, the tempo of the tune was given as 1/8=132. For some reason unknown to me, ABC Navigator changed that to 1/4=200. The dancers would have been knackered! Additionally, the key given in Jack's file was "K:A Mixolydian". Since parsers should ignore spaces, this should have been interpreted the same as "K:AMix". Instead the program put it in a completely arbitrary key hardly recognizable as the same tune.

I also tried the same tune from several iterations in JC's Tune finder and all of them sounded the same as Jack's file with minor tempo variations, so my conclusion is that ABC Navigator isn't the program for me.