layout problem

[Archer Endrich]

Hello,

I've been given a short item to realise in Lilypond and it includes a 
layout problem that I haven't been able to solve.

Basically, it is a piano piece in which, after a bit, a part for chimes 
is added:  i.e., another staff above the piano's treble part a few bars 
in as in my MWE.  I have tried to do this as an ossia staff in 
testlayoutB.ly  but it produces the result testlayoutB.pdf which starts 
the chimes part at the beginning of the example, not where I want it to 
start.

Comments in my .ly refer to a semicolon being commented out and 
reinstated just above the piano Bass clef part.  This causes the chimes 
and piano treble second line line to begin where I want it to, but it is 
placed below the bass, with a spurious clef above the bass.

What I would really like to do is to use StaffGroup as in testlayoutA.ly 
but this fails with a fatal error: "\new StaffGroup  %Fatal error: 
'spurious expression in \score'", so Lilypond rejects this kind of 
construction.

I have a voice & piano piece of my own which changes the number of 
staves in the piano part, so I'm very keen to learn how to deal with 
changing numbers of staves in a score.

Thanks!

Archer

testLayoutB.ly
Description: Text Data

testLayoutA.ly
Description: Text Data

testLayoutB.pdf
Description: Adobe PDF document