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: