copyright = \markup {
  \with-url #"https://creativecommons.org/licenses/by-sa/4.0/" \line {
    CC BY-SA 4.0
  }
}
tagline = \markup {
  \with-url #"https://euandre.org/music.html" \line {
    euandre.org/music.html
  }
}

rall = {
  \override TextSpanner.bound-details.left.text = "rall."
  \override TextSpanner.bound-details.right.text = "a tempo"
}