I was wondering if the metronome number in a \tempo command could be a scheme number. This would make it easier to do effects for fermata and ritards and relative tempo changes, in midi files.
For example, it would be nice to be able to do something like this:
---------------- #(define base-tempo 100)
\tempo 4 = #base-tempo
% some music % insert markup for "half note = dotted quarter" metronome mark % and override so the following is invisible in the score