I was playing some piano music today, and saw that familiar notation "D.S. al Coda". Although it was familiar, I didn't actually know what it meant. I knew it had to do with going back and repeating some part of the music, but that detail of my piano education had withered long ago.
So I looked it up online, finding this great online music notation reference: Music Theory Online. Chapter 24 is Repeats, and told me what I needed to know. Acoustic Guitar also has a handy online lesson about notation. So: "D.S. al Coda" means go back to the percent-over-S sign, then play to the other plus-over-O sign, then play the coda (the end).
But when I looked at my sheet music with this new understanding, I saw some oddities: First, the percent-over-S sign was placed at the beginning of the piece, so why not use "D.C. al Coda", which means go back to the beginning, and so on? And when I looked at the end of the piece, it seemed clear it could have been written more compactly without changing the music: the same measures were in the coda as in the normal repeat that was skipped.
I guess music can be refactored just as code can. What I saw in the music were duplicate lines of code that could have been eliminated by rewriting the loops with different termination conditions! Fascinating.
BTW: Back in March, I asked about MIDI-to-notation converters. I really appreciate the shorthands of music notation after looking at the output of these programs. All the loops have been unrolled, all the trills, grace notes, and arpeggios have been literalized, and so on. A simple three-page song becomes a twelve-page mess of mind-numbing repetitive scribbles.