\book again

[Graham Percival]

I know that identifiers must be at the toplevel of a .ly file, but do 
book-wide \context{} changes also need to be at toplevel?  I couldn't 
find a way to define them inside a \book -- lilypond complained whether 
I used \paper{} or \layout{}.

identifier = { c'4 }
\layout {
        \context { \Voice % applies to all scores
                \override TextScript #'padding = #1.0
        }
}
\book {
        \version "2.9.8"
        \score {
                { c'4 \identifier }
                \layout{
                        \context { \Voice % applies to only this score
                                \override Glissando #'thickness = #3
                        }
                }
        }
        \score {
                { c'4 }
                \layout{}
        }
        \paper {}
}