GrandStaff name ?

[Meixner Music]

Hello all!

First a big Thank You to the developers of lilypond:
I'm a seasoned music type setter and went through all of Finale to 
Graphire Music Press (which did beautiful output - not as good as 
lilypond of course - and regrettably died some time ago). Now I'm just 
digging through the concepts and trying everything.

Hopefully the gurus can help me with this:
I build a little template for strings, with the violins named as group 
("Violini") and "1." and "2." for individual staves. Now 
"GrandStaff.instrument = "...." doesn't appear in output - if I use 
PianoStaff with PianoStaff.instrument everything's ok, but I don't need 
the special spacing of a piano staff here...

...see a short example below, showing both methods - what am I 
overseeing?

=======

\paper {raggedright = ##t}

\score {
        \new StaffGroup {
                <<
                \new GrandStaff {
                        \set GrandStaff.instrument = "Violini  "
                        <<
                        \new Staff {
                                \set Staff.instrument = "1."
                                {\clef violin c''1}
                        }
                        
                        \new Staff {
                                \set Staff.instrument = "2."
                                {\clef violin e'1}
                        }
                        >>
                }
                
                \new PianoStaff {
                        \set PianoStaff.instrument = "Violini  "
                        <<
                        \new Staff {
                                \set Staff.instrument = "1."
                                {\clef violin c''1}
                        }
                        
                        \new Staff {
                                \set Staff.instrument = "2."
                                {\clef violin e'1}
                        }
                        >>
                }
                
                \new Staff {
                        \set Staff.instrument = "Viola"
                        {\clef alto g1}
                }
                
                \new Staff {
                        \set Staff.instrument = "Violoncello "
                        {\clef bass c1}
                }
                >>
        }
}