\version "2.11.64-1"

global = {
  \key c \major
  \time 4/4
}

upper = \relative c'' {
  \clef treble
  a4 b c d
}

lower = \relative c {
  \clef bass
  a2 c
}

dynamics = {
  \override TextSpanner #'bound-details #'left #'text = #"acc. "
  s2.\startTextSpan s4\stopTextSpan
}

pedal = {
  s2\sustainOn s\sustainOff
}

\score {
  \new PianoStaff = "PianoStaff_pf" <<
    \new Staff = "Staff_pfUpper" \upper
    \new Dynamics = "Dynamics_pf" \dynamics
    \new Staff = "Staff_pfLower" << \lower >>
    \new Dynamics = "pedal" \pedal
  >>

  \layout {
    % define Dynamics context
    \context {
      \type "Engraver_group"
      \name Dynamics
      \alias Voice
      \consists "Output_property_engraver"
      \consists "Piano_pedal_engraver"
      \consists "Script_engraver"
      \consists "New_dynamic_engraver"
      \consists "Dynamic_align_engraver"
      \consists "Text_engraver"
      \consists "Skip_event_swallow_translator"
      \consists "Axis_group_engraver"
      \consists "Text_spanner_engraver"

      pedalSustainStrings = #'("Ped." "*Ped." "*")
      pedalUnaCordaStrings = #'("una corda" "" "tre corde")
      \override DynamicLineSpanner #'Y-offset = #0
      \override TextScript #'font-size = #2
      \override TextScript #'font-shape = #'italic
      \override VerticalAxisGroup #'minimum-Y-extent = #'(-1 . 1)
      
      
  \override TextSpanner #'bound-details #'left #'stencil-align-dir-y = #CENTER
    }
    % modify PianoStaff context to accept Dynamics context
    \context {
      \PianoStaff
      \accepts Dynamics
    }
  }
}

\score {
  \new PianoStaff = "PianoStaff_pf" <<
    \new Staff = "Staff_pfUpper" << \global \upper \dynamics \pedal >>
    \new Staff = "Staff_pfLower" << \global \lower \dynamics \pedal >>
  >>
  \midi { }
}