Vertical Spacing

[Jonathan Wilkes]

Hello,
     How do I say: "Hey Lilypond, use 
the following 'minimum-Y-extent for whatever system m. 2 ends up in."

I don't see anything in the LM about this, and NR 4.4.1 doesn't make it 
clear that the following override only sets the 'minimum-Y-extent at the 
beginning of the piece or in a \layout block.

-Jonathan

Snippet:

% Created on Wed Sep 23 22:27:52 EDT 2009
\version "2.13.3"

staffPiano = \new PianoStaff {
        \set PianoStaff.midiInstrument = #"acoustic grand"
        \set PianoStaff.instrumentName = #"Piano  "
                \time 4/4
                                <<
                \context Staff = "RH" { 
                        \clef treble
                        \key c \major
                        \relative c' {
                                c d e f
                                c d e f
                                c d e f
                        }
                }
                \context Staff = "LH" {                         
                        \clef bass
                        \key c \major
                        \relative c {
                                c d e f
%                               \break
                                \once \override Staff.VerticalAxisGroup 
#'minimum-Y-extent = #'(-4 . 10)
                                c d e f
                                c d e f
                        }
                }
        >>
}

\score {
        <<
                \staffPiano
        >>
}