\version "2.19.40"

\language english

\layout {
  \context {
    \Voice
    \consists "Horizontal_bracket_engraver"
  }
}

\relative c'' {
  \clef treble
  \key g \major
  \override HorizontalBracket.direction = #UP
  \override Score.BarNumber #'break-align-symbols = 
    #'(staff-bar clef)

  \override HorizontalBracket.outside-staff-priority = #1
  % \override TextScript.avoid-slur = #'inside 
  g2\(\startGroup^\markup a g4. g8 | % this markup should be above the bracket
  ef'2. d4 c2 g |
  af1\)->\stopGroup |
  g2\(\startGroup^\markup a' g4. g8 |
  ef'2. d4 |
  c2 af4. af8 |
  bf1\)->~ |
  bf2 r\stopGroup |
  bf2.\startGroup^\markup b bf4 |
  c2 c4. c8 |
  df1~ |
  df2 r\stopGroup |
}