Accidental in brackets

[Urs Liska]

Hi all,

I don't seem to find the right thing, neither in the docs, the LSR nor
the list archive. I need to put square brackets around some accidentals
in order to differentiate them from default parentheses.

I don't find the way to create the respective stencil for this.

It has to be possible to do that \once, and I assume I'll run into the
situation where I will need both round and square ones within a chord.

Any help available?

Thanks
Urs