Is there an "official" way of marking a section of measures as optional? I'm not talking about an ossia, but defining a whole consecutive set of measures as "include according to preference".
I'm transcribing a piece with quite a large intro, which consists of three sections, each adding either a layer or a twist to the theme. In practice, any combination of those (as long as you keep the order) can be used, and any combination can actually be found in renditions of the piece.
Is there way to properly annotate this in sheet music, other than textual instructions to the player?