Re: Inserting a verical space, or an empty line, between two markups attached to a note.

[Noeck]

% Perhaps something like

\header {
  tagline = \markup \center-column { "Rome" "Mars 1934" }
}

{ c''1^\ppp_\markup \italic \center-column { "m. d." "dessus" }

  \override Score.RehearsalMark.direction = #DOWN
  \override Score.RehearsalMark.font-size = -1
  \override Score.RehearsalMark.self-alignment-X = #RIGHT
  \mark \markup \center-column { " Rome " "Mars 1934"}
  \bar "||"
}