Hiding empty staves

[Andrew Bernard]

I have a two stave piece using a PianoStaff. In some sections I need to hide the unused lower stave for a number of bars. Using \RemoveEmptyStaves or \RemoveAllmptyStaves does nothing. There are only spacer rests in the staff in question.

The NR in Section A.20 says these functions 'Remove staves which are considered to be empty according to the list of interfaces set by keepAliveInterfaces, including those in the first system.’ But what does it mean for a staff to be considered empty?

Andrew