On 10 Nov 2004, at 06:34, Remo D. wrote:
I realized that the overlay operator & is the only one that moves the time backward.
I think the 2.0 standard is not very clear on this operator, I'll try to summarize how it will implemented in ABCp, of course everything is subject to discussions and comments from your side!!
Reading both the standard and the abcm2ps docs I understood the syntax should work as follows: (a=b means "a is vertically aligned with b")
1) & splits a measure GA | bc & de | Fg --> d = b, e = c
OK.
2) Duration counts! GA | bc & e2 | Fg --> e2 = b
OK.
3) overaly may occur on multiple measures G(&A | bc & d | F&)g --> d = A, F = b, g = c
No, I think the & operator sets the time back to the bar line, so this should be A=G d=b (bar doesn't add up) and g=F.
Or have I got the wrong end of the stick?
but some questions are left unanswered:
1) What is durations don't match? Should we add rests or give an error?
GA | b & de | Fg --> d =b, e=?
Definitely give an error. If the user really wants |[bd] e | here he can write that, or use an invisible rest | b x & de |.
2) The example on the abc2.0 standard page seems to suggest that the & operator splits the line and not the measure. I assume the example is from an old proposal and should be read as:
(&g4 f4 | e6 e2 &\ (d8 | c6) c2 &)
I don't understand that either.
3) The abc2.0 standard present it as "voice overlay" but they do not really defines a separate voice (as the V: field does), correct?
Yes. It's a way of writing overlapping chords within a single voice.
4) What's the meaning of &&? I found it in a couple of examples around.
An error? I haven't a clue.
5) Anything else I missed on overlays?
Let me know your thoughts.
MusicXML has an equivalent <backup> operator which takes a numerical value which indicates how far the time point should be backed up. The time point may not be backed up further than the previous bar line. There is also a matching <forward> tag, which is essentially an invisible rest. Unfortunately these get horribly over used, so that a piano part where several voices are being played by one hand will be written with that hand all in one voice, with lots of <backup> and <forward> tags in each measure. The result is impossible to read and also tricky to parse. Let's not go there!
Phil Taylor
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