midiChannelMapping (introduced in 2.14) not documented in NR

[Federico Bruni]

Dear Bug Squad

I don't want to push you but I think that you may have missed this 
report, hidden inside a reply to a question made in lilypond-user:
http://lists.gnu.org/archive/html/bug-lilypond/2012-11/msg00112.html

I think that midiChannelMapping is not properly documented.
It is listed in the context properties appendix:

midiChannelMapping (symbol)
How to map MIDI channels: per instrument (default), staff or voice.

But I can't find any place in the NR where its usage is explained.
All I can find is the explanation here:
http://lilypond.org/doc/v2.14/Documentation/changes/index.html

Thanks
--
Federico