Volta text markup using repeatCommands

Though volte are best specified using \repeat volta, the context property repeatCommands must be used in cases where the volta text needs more advanced formatting with \markup.

Since repeatCommands takes a list, the simplest method of including markup is to use an identifier for the text and embed it in the command list using the Scheme syntax #(list (list 'volta textIdentifier)). Start- and end-repeat commands can be added as separate list elements:

\version "2.24.0"

voltaAdLib = \markup { 1. 2. 3... \text \italic { ad lib. } }

\relative c'' {
  c1
  \set Score.repeatCommands = #(list (list 'volta voltaAdLib) 'start-repeat)
  c4 b d e
  \set Score.repeatCommands = #'((volta #f) (volta "4.") end-repeat)
  f1
  \set Score.repeatCommands = #'((volta #f))
}