GrandStaff Name

[Will Oram]

Forgot to ask this the first time around. :P

The trick of naming a GrandStaff (instead of each staff within) has 
been around for awhile (see 
http://lilypond.org/doc/v2.7/input/test/out-www/lily-899083229.ly), but 
for the life of me I can't reproduce the effect myself.

I tried

\new GrandStaff <<
                                \new Staff <<
                                        \set GrandStaff.instrument = #"Violons"
                                        \set GrandStaff.instr = #"Vln."
                                        \new Voice \relative dflat'' { 
\mIViolinOne }
                                >>
                                
                                \new Staff <<
                                        \new Voice \relative dflat'' { 
\mIViolinTwo }
                                >>
                        >>

...but got nothing in the output. It looks more or less like the 
snippet, says I.

Will Oram // Genius @ Large // AIM spamguy21
spamguy (at) foxchange (dot) com // wro1 (at) cwru (dot) edu