\paper { ragged-right = ##f }

\relative c'' {
  \override TextSpanner.bound-details.left.text = #"bla"
  \override TextSpanner.bound-details.right.text = #"blu"
  a4 \startTextSpan
  b4 c
  a4 \stopTextSpan

  \override TextSpanner.style = #'line
  \once \override TextSpanner.bound-details.left.stencil-align-dir-y = #CENTER
  a4 \startTextSpan
  b4 c
  a4 \stopTextSpan

  \override TextSpanner.style = #'dashed-line
  \override TextSpanner.bound-details.left.text =
    \markup { \draw-line #'(0 . 1) }
  \override TextSpanner.bound-details.right.text =
    \markup { \draw-line #'(0 . -2) }
  \once \override TextSpanner.bound-details.right.padding = #-2

  a4 \startTextSpan
  b4 c
  a4 \stopTextSpan

  \set Staff.middleCPosition = #-13
  \override TextSpanner.dash-period = #10
  \override TextSpanner.dash-fraction = #0.5
  \override TextSpanner.thickness = #10
  a4 \startTextSpan
  b4 c
  a4 \stopTextSpan
}