NR and allocating tweak command to variable

[Nick Payne]

I was trying to allocate a tweak command to a variable and eventually 
managed to get it to work after finding what I needed by a search of the 
lilypond-user archives ( 
http://lists.gnu.org/archive/html/lilypond-user/2011-09/msg00279.html).

However, I was initially misled by the NR having a section named "Using 
variables for tweaks ": 
http://www.lilypond.org/doc/v2.17/Documentation/learning/using-variables-for-tweaks, 
but this actually deals with using variables for overrides, and should 
maybe be renamed as "Using variables for overrides".

The code that I got to work is below:

\version "2.17.14"

fia = #(define-music-function
  (parser location grb)
  (ly:music?)
#{
  -\tweak script-priority #-199 -$grb
#})

\relative f'' {
  \set fingeringOrientations = #'(left)
  <cis-1 a-1 e-1>4
  <cis!-1 a-1 e-\tweak script-priority #-199 -1>4
  <cis!-1 a-1 e-\fia-1>4
}