Hi Frédéric:
Halas, for StaffGroup, the trick works but the spanners are
all at the top of the score, not above each StaffGroup.
Maybe this hint will help you solve the problem:
\version "2.12.2"
\layout
{
\context
{
\type "Engraver_group"
\consists "Text_spanner_engraver"
\consists "Axis_group_engraver"
\name "ConTextSpan"
\override VerticalAxisGroup #'minimum-Y-extent = #'(1 . 3)
}
\context { \Score \accepts ConTextSpan }
\context { \Voice \remove "Text_spanner_engraver" }
}
stringendo = { \textSpannerUp \override Score.TextSpanner #'(bound-
details left text) = "Stringendo" }
\score
{
<<
\new ConTextSpan { \stringendo c'1 \startTextSpan \repeat unfold 4
{ c' } c'\stopTextSpan }
\new StaffGroup
<<
\new Staff { \stringendo c'1 \startTextSpan \repeat unfold 4
{ c' } c'\stopTextSpan }
\new Staff { \stringendo c'1 \startTextSpan \repeat unfold 4
{ c' } c'\stopTextSpan }
>>
\new ConTextSpan { \stringendo c'1 \startTextSpan \repeat unfold 4
{ c' } c'\stopTextSpan }
\new StaffGroup
<<
\new Staff { \stringendo c'1 \startTextSpan \repeat unfold 4
{ c' } c'\stopTextSpan }
\new Staff { \stringendo c'1 \startTextSpan \repeat unfold 4
{ c' } c'\stopTextSpan }
>>
>>
}
Bonne chance!
Kieren.