\version "2.12.2"
\clef "treble_8"
\relative c {b'16 d g b e
\textSpannerDown
\override TextSpanner #'bound-details #'left #'text = #"XII "
g16\startTextSpan
b16 e g e b g\stopTextSpan
e16 b g d}
\relative c {b'16 d g b e
#(set-octavation 1)  \set Staff.ottavation = \markup { \upright {\tiny "XII" } }
  \override Staff.OttavaBracket #'dash-period = #0.2 g'16 b16 e g e b g#(set-octavation 0)  
e,16 b g d}