ottava =
#(define-music-function (parser location octave) (integer?)
   (_i "Set the octavation.")
   #{
     #(make-music 'OttavaMusic 'ottava-number octave)
     \set Staff.ottavation =
     #(if (< octave -1) #{ \markup \concat { #(number->string (+ 1 (* -7 octave))) \fontsize #-2 "mb" } #}
      (if (= octave -1) #{ \markup \concat { "8" \fontsize #-2 "vb" } #}
      (if (= octave +0) #f
      (if (= octave +1) #{ \markup \concat { "8" \fontsize #-2 \translate-scaled #'(0 . 0.85) "va" } #}
                        #{ \markup \concat { #(number->string (+ 1 (* 7 octave))) \fontsize #-2 \translate-scaled #'(0 . 0.85) "ma" } #}
      ))))
   #})


% example

% layout settings for bold dotted lines (does not fully work as expected)
%\layout {
%  \override Score.OttavaBracket #'style = #'dotted-line
%  \override Score.OttavaBracket #'thickness = #2
%  \override Score.OttavaBracket #'font-series = #'bold
%}

\new Staff \relative c''' {
  \ottava #1 a a
  \ottava #-1 a,, a
  \ottava #2 a''' a
  \ottava #-2 a,,,, a
  \ottava #3 a''''' a
  \ottava #-3 a,,,,,, a
  \ottava #0
}