Using one identifier or another

[Johan Vromans]

Hi,

In a template file I want to check if a particular identifier has been
defined, and act accordingly.

For example:

  \score {
    \allMusic
    \layout {
    }
  }

  \score {
    \unfoldRepeats  \allMusic
    \midi {
    }
  }

In the MIDI block, I would like to use identifier allMusicForMIDI if
that has been defined, otherwise use the allMusic as indicated above.

Is there an easy (and documented) way to accomplish this?

-- Johan
   Chord is alive! http://chordii.sourceforge.net