Staff "reappearance" callback?

[Kieren MacMillan]

Hi all,

Michael's question about instrument names got me wondering...

Is there an easy way to have a callback for any grob (e.g. TimeSignature) so 
that it knows whether or not its Staff context was alive in the previous 
system? If so, this would have lots of good uses, including Michael's two 
features:
    1. Make the InstrumentName take the long name each time a Frenched staff 
reappears.
    2. Make the TimeSignature appear each time a Frenched staff reappears.

Thanks,
Kieren.