How to specify optional repeats/volta

Question

Is there a widely-accepted and succinct way to indicate that a repeat and/or volta is optional, or to indicate that a section should be repeated n times where n is up to the player (within bounds)?

I want to be able to say things like

• repeat this bar/section between 3 and 7 times
• choose (zero or) one of these two voltas on the last repeat
• play section A, then one of sections B,C,D, then section E and/or F
• Da Capo if you feel like it al fine uno or fine due

so that the structure of the piece is semi-improvised, but I want to avoid cluttering the score with lots of written instructions.

I imagine contemporary classical composers and jazz musicians must do this sort of thing all the time, but I'm not very familiar with either world.

I use LilyPond and don't mind writing my own functions (within reason). At the moment I'm only interested in the typeset music looking right, I don't want to control midi output or Denemo playback or anything like that.

Answer 1

When I've encountered optional repeats, it's pretty much always been specified in text about the repeat ("opt. repeat", or similar).

I'd suggest using short text, because it's pretty unambiguous. Symbols are only good when they are widely understood. Of course, you'll want to keep any text short and clear. You could also add a longer note about the piece structure at the start of end if the piece.

I've also run into "D. S. ad Nauseum", but that's not entirely conventional.