{
  \key a \major
  \set Score.markFormatter = #format-mark-box-letters
  \once \override Score.RehearsalMark.outside-staff-priority = #5000
  \once \override Score.RehearsalMark.self-alignment-X = #LEFT
  \once \override Score.RehearsalMark.break-align-symbols = #'(key-signature)
  \mark \markup { \bold { Senza denti } }

  % the hidden measure and bar line
  % \cadenzaOn turns off automatic calculation of bar numbers
  \cadenzaOn
  \once \override Score.TimeSignature.stencil = ##f
  \time 1/16
  s16 \bar ""
  \cadenzaOff

  \time 4/4
  \once \override Score.RehearsalMark.self-alignment-X = #LEFT
  \mark \markup { \box \bold Intro }
  d'1
  \mark \default
  d'1
}