\version "2.15.27"
%\version "2.15.28"
%% Span -----------------------------------
%% Syntaxe: \bbarre #"text" { notes } - text = any number of box 
barre= #(define-music-function (barre location str music) (string? ly:music?)
           (let ((spanned-music 
                   (let ((first-element #f)
                         (last-element #f)
                         (first-found? #f))
                     (music-map (lambda (m)
                                  (if (eqv? (ly:music-property m 'name) 'EventChord)
                                      (begin
                                        (if (not first-found?) 
                                            (begin
                                              (set! first-found? #t)
                                              (set! first-element m)))
                                        (set! last-element m)))
                                  m)
                                music)
                     (if first-found?
                         (begin
                           (set! (ly:music-property first-element 'elements)
                                 (cons (make-music 'TextSpanEvent 'span-direction -1)
                                       (ly:music-property first-element 'elements)))
                           (set! (ly:music-property last-element 'elements)
                                 (cons (make-music 'TextSpanEvent 'span-direction 1)
                                       (ly:music-property last-element 'elements)))))
                     music)))
             (make-music 'SequentialMusic
               'origin location
               'elements (list #{
			\once \override TextSpanner #'style = #'line 
                        \once  \override TextSpanner #'bound-details =  #'((left (Y . 0) (padding . 0.25) (attach-dir . -2)) (right (Y . 0) (padding . 0.25) (attach-dir . 2))) 
                        \once  \override TextSpanner #'bound-details #'right #'text = \markup { \draw-line #'( 0 . -.5) }
                       \once  \override TextSpanner #'bound-details #'left #'text =  \markup {  $str }                    
                          #}
    spanned-music)))) 

\relative c' { 
  \barre #"BI" { f,4 bes es g }  
  c c c\startTextSpan c c\stopTextSpan
}